There are six Darshan Shashtras - also known as Upaang or Shat Darshan (The Six Visualisation); they are:-
Purva Mimaansa / Mimaansa Shashtra by Rishi Jaimini:- The author of this Darshan is Rishi Jaimini ji. The science of morals is discussed in detail. The concept of this darshan is Dharma, Dharmi (the thing which possess dharma) & Yagya (Sacrifice) & the duties & non-duties of the mankind which range from family life to national service are described, through which the extreme development of the entire nation is possible. Infect the great form of the Dharma is the Yagya (Sacrifice).
Vaisheshika Shashtra by Rishi Kannaad:- The author of this Darshan is Rishi Kanaad ji. He has described the true form of the Dharma. The mean that is helpful in achieving worldly & spiritual success is Dharma. Moksha ( Supreme Bliss) is obtained by living as truly righteous life & thereby getting the soul purified & exalted, and gaining a true conception of the six entities, viz., Noumenom, Attribute, Action, Commonness, Dissimilitude & Inherent relation, ( as of cause & effect, of whole with its parts). Its main themes are "Nothing can be created without any material', "Absence of the cause is absence of the effect", etc.
Nyaaya Shashtra by Rishi Gautam:- The author of this Darshan is Rishi Gautama ji. The subject of this darshan is to attain Moksha (Salvation) by getting the philosophical knowledge of 16 (sixteen) objects like Proof/Evidence, Proposition, Logic etc., The order in which the above 16 objects explained is as follows (i) Name (ii) Features & (iii) Detailed examination of the objects. Its main theme is " To examine the things through the proofs & evidences is Nyaaya". God is the creator of the universe, formless, omnipresent, Soul is different from the body, mind etc., & material nature is unintellect & raw material of the universe are clearly explained & proving the Traitavaad. An ancient & authentic commentary on this darshan by Maharishi Vaatsyayan ji is available.
Yoga Shashtra by Rishi Patanjali:- The author of this Darshan is Maharishi Patanjali ji & it deals with the Saadhana, Dhyan, Samaadhi etc., & gives a clear-cut idea about the God, Soul & Material world, true form of the God, Vedic worship (Upaasanaa) & Means of obtaining the Moksha (Salvation). Further subtle topics are also explained like, (i) what is yoga ?, (ii) What is the reason of soul's bondage ?, (iii) what are the different stages & attainments of the yoga practitioner (Saadhak) ?, (iv) what are the fluctuations of the mind & how to completely stop it ?, (v) Till what time the connection of the soul & mind exists? etc., An ancient & authentic commentary on this darshan by Maharishi Vyaasa ji's is very familiar in yoga.
Sankhya Shashtra by Rishi Kapil:- The author of this Darshan is Rishi Kapil ji & its subject is about the Prakriti & its products & Purusha. It is absorbed that the word "Purusha" is denoted for both the God & the Soul. The basis of this darshan is Sat Kaarya Vaad "Nothing can ever become something , nor can something ever become nothing". The order of Creation & Dissolution of the universe from the Prakriti is exclusively explained in this darshan. Only through discrimination obtained by knowing the true form of the material world & purusha, Moksha/Salvation is obtained. It is also explained that the universe is not false, True in existence by having the material world as the subtle cause & further 24 (Twenty Four) intermediate entities.
Uttar Mimaansa / Vedaant Shashtra by Rishi Veda Vyaas / Baadaraayana:- The author of this Darshan is Rishi Vyaasa ji & the subject is about the Brahmaa (Iswhar) & attainment of Brahmaa / Moksha (Salvation). Its other names are Brahmasootra & Uttar Meemaamsaa. Brahmaa (God) is an entity, which is omnipotent, omnipresent, blissful. He is free from sorrows of birth & death. Jeevaatmaa (Soul) is also a different entity having little intellect & subtle. He wants to get rid out of sorrows. God creates the universe from the Prakriti. The meaning of the Vedaanta is - "The essence of the Vedas".
In short some few common principles of the six Darshans :
By the freedom, from the three types of sorrows, Moksha (Salvation) is obtained.
God, Soul & Prakriti are the eternal causes of the creation of the universe.
Nonexistence of Existent objects & existence of nonexistent objects is extremely impossible.
Vedas are self-proven, because it is gospel-word of the God.
Soul is different from the body,mind etc., & inconsequential.
God is different from the soul, omnipresent, infinite intellect, omnipotent etc.,
According to the God's discipline & deeds done by the soul, the soul repeal the results of the deeds.
The visible universe is the product of the Prakriti.
The reason of the bondage of the soul is its ignorance.
Each & Every body has its own unique soul.
Soul can never become a God, it has its own unique existence.