You might look into some of the classic Steve Jackson and Ian Livingstone Fighting Fantasy books. While it's hard to classify any books of this sort as for "adults", these definitely skewed older, and were built around a simple RPG system with rules for self-determining combat using dice, although they could just be read as traditional CYOA. There were fantasy, sci-fi, and supers settings. I think many have been reprinted.

Choose Your Own Adventure books for adults are tabletop RPGs

I have two words, "Lone Wolf".... although technically for teens, it does have some very violent themes in many of its books (so its probably as close as you can get).  Also, it is probably the best Choose Your Own Adventure series ever writen (At least book 4 and after.... the first 3 books are OK, but unless you have a very good imagination they can be pretty dry), there are about 28 books in the series. 

Its based on a D20 system, and has character design (which many choose your own adventure books lack).... the abilities you choose for your character play a role in which choices you can make.  Do you want to have a sixth sense for danger and never fall into abushes, or be able to blast your oponents mind with telepahy and improve you combat effectivness.  Everytime you finish a book in the series your character "levels up" and gains a new ability.

Its a fantasy genre.

http://www.gamebooks.org/lonewolf.htm

Anyway... check it out.   

*Edit*

 Also.... you can download many of the books for free (apparently) at this website.

http://www.projectaon.org/

I thought everybody read these?  They should.  The entire series can now be "played" online.

http://www.projectaon.org/staff/eric/lw01.htm

World map > http://outspaced.fightingfantasy.org/Hosted/Jan_Charv%C3%A1t_Magnamund.png

http://www.projectaon.org/en/statskeeper/

http://www.projectaon.org/en/Main/FlightFromTheDark

This, I just found - http://lonewolfthegame.com/video.html