Most of us living in India, take Indian culture  and philosophy for granted. When I asked a friend of mine to review a  recently launched culture website, she said it was lovely but her  non-resident Indian friends would find it more interesting. It’s  only when we become global citizens and start interacting with people  from various countries and cultures, do we wish to know more about  India and its philosophy in particular. 
This  article is a precis of a chapter from the book Seven  Systems of Indian Philosophy by Pandit  Rajmani Tigunait, Ph.D. I have added insights too. 
Indian  philosophy is inward looking, and aims to help human beings deal with  ups and downs of life with the goal of self-realization. 
The Sanskrit word for philosophy is darsana, which means direct vision. The words symbolize the difference between  modern Western philosophy, which mainly relies on an intellectual  pursuit and Indian philosophy that relies on a direct vision of truth  and pure Buddhi (reasoning). 
Darsana is divided into two categories namely-  Astika (believer in the Vedas) and Nastika (non-believer in the  Vedas). Astika are Nyaya, Vaisheshik, Sakhya, Yoga, Mimamsa, and  Vedanta. Nastika are Carvaka, Jainism and Buddism. Others are a  mixture of the ideas of these systems. Although each school of  philosophy is unique, they all have some common characteristics. Some  of the important ones are - 
Direct  experience: All systems of Indian philosophy  claim to be derived from the Veda but the Veda itself is a record of  the sages who realized the truth within. To solve life’s questions  related to nature of life, death, birth, and cosmic or individual  existence, they started making rational inquiries and observations.  Unable to find satisfactory answers, they discovered various methods  of meditation that help one attain higher levels of consciousness in  which one may directly experience the truth. Each school originated  with an enlightened teacher who described his experiences of the  truth and method of attaining it.
Acceptance  of authority: Respect for sages and ancient  scriptures is a strong tradition in India. When a teacher advocates a  new philosophical system, he cites established scriptures or the  writings of authorized sages to support his statements. The Astika or  orthodox schools always refer to the Veda to support their theories.  The Nastika or unorthodox schools follow the authority of their  founder. Buddha, for example, reiterated many things said in the Veda  but did not cite the Veda as the source of his views. Hence, the  tendency to rely on the work of a realized teacher is maintained in  Buddhism, too. 
Scholar  and former President of India Dr S Radhakrishnan wrote in volume 1 of  Indian Philosophy about what is common to  Upanishadic and Buddhist thought. He also said that  the four noble  truths of Buddhism correspond to the four truths of Samkhya.
Harmony  among schools: All systems of Indian  philosophy have a unique quality of cooperating with one another.  During a debate, the intent is not to destroy another’s philosophy  but to clarify one’s own theories and thoughts. This has enabled  various schools to live in harmony. Indian philosophers realized that  every human mind is unique and it must be allowed to follow a  philosophy of its choice. 
Parallel  growth and coexistence of various schools: The  various systems of philosophy flourished and grew simultaneously. The  reason is that the open-minded approach attracted students of various  hues who were impressed with the practical aspects of that system of  philosophy. When a particular teacher delivered a message, it was  studied and teachings were put into practice by a group of people  whom it suited. Thus, was formed a School of Philosophy. Each system  continued to coexist because it provided a theoretical and practical  philosophy to meet intellectual and emotional needs of the students  at different levels of realization. 
There is  Saivism in Kashmir and Kerala, and Vaishnavism, Shaktism, and Yoga  throughout India. These five schools of Vedanta exist till date. All  these systems continue to undergo change and grow to meet the needs  of modern man without deviating from the basic teachings of their  founders. Followers of a sect do not fight with each other. Instead a  student of another school is to be defeated on the strength of  intellectual arguments rather than by using a gun. 
Open-mindedness: A broad outlook that reflects its unflinching devotion to truth  distinguishes Indian philosophy. Each school is open to views of all  other schools. It was nothing like there is a best way to achieve  self-realization. The established system of philosophical exposition  in the Indian tradition involves explaining and criticizing the prior  view of the subject, then refuting the view and describing a  subsequent view that takes you to a higher level or final theory.  Because of a continuous exchange of ideas, the philosophical systems  have with time, become more sophisticated and complete. 
Simply  put, an individual who enters into a discussion with an open mind and  is willing to listen to another person’s point of view is likely to  have a better understanding of the situation. It is one of the  reasons why Indians have taken to Western culture so easily. We are  able to adjust in just about any environment, be it U.S., Australia,  Britain or South Africa. 
Support  of logic and reasoning: Direct experience is  the foundation of Indian philosophy, but reason and logic are the  chief tools that enable the system to develop and grow. The theories  are presented in a way that a rational mind can easily accept. All  systems of Indian philosophy apply the methods of logic to argue  their points of view and protect themselves from criticism. This  reason only justifies what intuition or experience has already  revealed. By virtue of being an important part of our philosophy,  logic got ingrained in the Indian mind. Since computer software uses  logic extensively, it has helped India gain recognition as a  potential global software power.
The  Belief of Eternity: Each system of Indian  philosophy proclaims that there is an eternal consciousness in man  and the realization of this consciousness is the goal of life.  Imperfections are a result of ignorance and are on the surface of our  personality but what needs to be done is, discovery of Self within,  that lies in a perfect state of bliss. Man’s physical existence  depends on his karma (actions) but the center of his life is eternal.
The Law  of Karma: Every Indian School accepts this  law which states that for every effect there is a cause, and for  every action, there is a reaction. If a man becomes attached to the  fruits of action, then he becomes a victim of his own karma because  it is the attachment to the results that motivate him to perform  future actions. The fruit has arisen out of the action and action out  of the fruit. This cycle is the wheel of karma. 
When the  only motivation to do something is enjoyment of the results, one is  bound to be unhappy because he will not always get what he wants. It  is the act of being more worried about the results than the act  itself. All schools agree that the concept of karma is the only  explanation for the existence of suffering. Nothing in life is  accidental, what we are today, is a result of our karma or deeds in  this or past life. A friend of mine has, with the help of astrology,  been able to know about acts and omissions of his previous life.  After discovering a substantial part of his inner self, he is able to  correlate the events of this life with his past lives. By connecting  between the past and present, births his perspective towards life has  changed. 
Karma is  not fate or kismat.  Karma means that every human being controls his future. You reap what  you sow. 
Moral  and ethical teachings: Ancient seers realized  that there must be some discipline in our lives with relations to  family, society, and nation for without law and order, the world  becomes disorganized resulting in misery. Eastern philosophers  believed that for peace within, there had to be peace outside. Lack  of morality and discipline creates misunderstandings in one’s  relationship with others and is the cause of emotional problems.  Emotions need to be disciplined and channelled correctly. Disciplines  related to the body and mind are generally known as moral and ethical  laws. The practical systems of Indian philosophy are based on these  laws. These are commitments, not commandments, accepted to create  external peace without which there can be no internal tranquillity.
Acknowledgement  of suffering: Most quests for  self-realization start with the reason behind pain and suffering. The  goal of each system is to overcome suffering. Buddha began his  philosophy by saying there is suffering, next he dictated that there  is a cause for it, there is a state in which suffering ceases and  finally there is a way to attain freedom from the pain. These  statements are called the Four Noble Truths. The pain and suffering  is due to our inability to experience the inner self. One suffers  because of one’s attachment with worldly objects. The moment we  start looking within, freedom from pain gets initiated.
Thoroughness: Because of this broad outlook, there is an  extreme thoroughness in Indian systems of philosophy. It is like the  river Ganga that originates from a glacier, runs down the hills of  Garwhal onto the plains of Uttar Pradesh, Bihar, and Bengal,  collecting water from different sources before it reaches the Bay of  Bengal and merges itself with the all embracing sea. 
Similarly,  Indian philosophy started with simple levels of human understanding,  incorporated the direct experiences of sages down the centuries to  become a vast and thorough body of knowledge. Tradition, respect for  ancient sages, and infinite quest for knowledge make Indian  philosophy so vast that it is difficult for people of other countries  to fathom how a group of men could have delved so deep into human  nature. 
Practicality: All  systems of Indian philosophy contain a practical aspect called  Sadhana. Thus, the theoretical aspects of philosophy can be applied  to everyday life. The ancient sages believed that any philosophy that  did not enable man to handle the problems of day to day to life was  of no use. People who have read the Bhagwad Gita would agree that the  holy book is not just about religion, but tells us how to handle the  crests and troughs of life.
Self-realization, the direct  experience of ones inner nature is the goal of all systems of Indian  philosophy. Every system prescribed its own way of overcoming pain to  achieve the ultimate goal. Thus, every human being has to look  within, understand his own nature, and figure out his path to  self-realization. It’s not like this is the only way. It’s all  about direct experience, as referred above. 
The way to reach this goal include  selfless love, service to others, purification, and self-control.  Because of their usefulness and practicality, each system of Indian  philosophy is as relevant today as it was when written thousands of  years ago. It is this quality of our philosophy that has enabled  India to survive through dark periods.
Also read 
1. Unconscious forces: a survey of some concepts  in Indian philosophy 
2. Why did  Buddhism vanish from India 
3. Shad  Darsanas - 6 systems of Indian philosophy