Aastika Nirishwarvāda that I adhere to - few notes

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1.PramaaNas -  three valid pramaaNas - pratyaksha, anumaana and shabda (vedvaakya). both for saamkhya and yoga.

vaisheshika, nyaaya and purva-mimaamsa hold four valid pramaaNas - pratyaksha, anumaana, upamaana, shabda.

vedaanta (notably advaita) hold six valid pramaaNas - pratyaksha, anumaana, upamaana, arthaapatti, anupalabdhi, shabda

All these six darshanas hold shabda aka shruti as a valid pramaaNa and consider it apaurusheya. Hence these six darshanas are called "aastika darshanas".

chaarvaka considers only pratyaksha as valid pramaaNa. naastika darshans (buddha and jaina) do not consider shabda (shruti) as a valid pramaaNa. they tried to build a parallel "shruti" wherein shabda means their shruti and not "the shruti". But it still was limited by being man-made.

read this link for more detailed exposition -
http://kalchiron.blogspot.in/2010/09/aastikas-and-naastikas-system-of.html

2, about Eeshvara - for saamkhya, yoga, purva-mimaamsa, nyaaya, vaisheshika - karma rules supreme. when all sanchita karma is exhausted, the seed of ahamkaara vanishes and kaivalya or moksha is attained spontaneously with termination of birth-death cycles. There is no need of an "external eeshvara" who is a "mukunda" (giver of moksha). various devi-devataas (kuladevata, ishTadevata, graama-devata et al) are to be worshipped as per needs or kulaachaara or time. With saadhana or aashirvaada of these devataas, some sequence of impending karma-phala can be altered (that is some good karma-phala which was due later can be brought ahead and current bad-karmaphala can be pushed ahead in time), but NO ONE has power to be above karma and absolve a karma-phala. Hence "eeshvara" is "not needed". Everyone HAS TO go through the phala of their karma, no matter what.

3. creation - no reference to eeshvara creating the existence. Existence Comes from prakruti who after coupling with purusha gives rise to mahat and in turn to ahamkaara that in turn gives rise to three guNas which in turn give rise to maanas, 5 karmendriyas, 5 gnaanendriyas, tanmaatra (5 senses and their analogous 5 mahabhutas) - thus srishti comes into existence. Why purusha coupled with prakruti in first place - don't know. vedaanta says it is leela of eeshvara. But that explanation not possible in this premise. it happens spontaneously.