Free Audiobooks No DRM No Cost No BS .....also superheroes

Well 99% is fiction on podiobooks so documentarys and actual science stuff are unlikely to be found on podiobooks. But i know another well recived podcast called hardcore hystory http://www.dancarlin.com/hardcore-history-series/ the free content is more than a few hours so if you like history that might be worth a try.
Back to podiobooks. General i would say everything above 80% is worth a try also the more reviews the better.

The science fiction part of podiobooks is quite big and diverse (almost 200 titles).
For example a scifi- thriller that is well liked would be The 7 th son antology. http://podiobooks.com/contributor/jc-hutchins/ . Not spacetravel scifi more like technology that dosent exist today existing today.

In the horror/scifi category i recommend Scott Sigler. His stuff is usually really bloody. He was among the first who gave his audiobooks away for free and gained enough reputation to even get his books in the New York Times best sellers list.
http://podiobooks.com/contributor/scott-sigler/
If you want to get a feel for his work take the short story collections Bones are White and/or Blood is red.(smal sidenote kissyman and the gentleman is one of my alltime favourites)

If you want something less action orientated i heartily recommend Nathan Lowells Trader Tales.
http://podiobooks.com/series/a-traders-tale-from-the-golden-age-of-the-solar-clipper/ a six book multiple award wining anthology.
This is more is in the spacetravel category. I quote a bit from a review by K.G.H. Nicholes who sums Mrs Lowells style of writing very fittingly
"Nathan Lowell gives me permission to enjoy "ordinary living" - doing what needs to be done, and finding pleasure in doing it ".