Nearly the entire Lone Wolf saga (20+ books) was donated and made freely available on https://www.projectaon.org, along two other minor series by the same author (one "Mad Max"-style postapocalyptic, and the other military-themed).

Lone Wolf was one of the best series in this genre back in the 1980's, and doesn't get nearly enough mention in comparison to the CYOA or Steve Jackson stuff.

They are long out of print, but I still have a soft spot in my heart for the GrailQuest series... a very loosely King Authur-themed series with a much more whimsical and campy style. I remember mailing the author a fan letter when I was about 10 years old, and receiving a very nice handwritten reply from Ireland (which I probably still have tucked in an old photo album somewhere). In the age of email, social media, and $50 autograph lines at cosplay conventions, younger people will probably never know the magic of contacting a favorite author and unexpectedly receiving a tangible reply later on.

Lone Wolf was great. Incorporated RPG elements, inventory that carried over between books, and a decent battle system that didn't require dice.

I've not read it yet, but the pop-culture/horror writer (and film critic) Kim Newman has a choose your own adventure book called Life's Lottery that lets you make life desicions for the protagonist as he grows up starting from childhood in 1960s England. It gets good reviews on Amazon and his stuff is usually good.

I highly recommend Life's Lottery. It's a nostalgic return to 80's Britain that should be entertaining even for anyone who didn't live through those years.

The fact that you control the choices of a person from childhood to adulthood, with astonishingly different outcomes depending on those choices, has the sublime effect of making you consider the direction your real life is going, and how your everyday trivial decisions shape it. Sometimes what appears to be a minor choice or even an evil decision can lead to a better outcome than the alternative.

New paperback and ebook editions were released a few years ago.

I don't know about _book_ books, but if I take your question more generally to mean any interactive fiction, then I would heartily recommend Counterfeit Monkey from Emily Short, or the 80 Days from Inkle. Both are a beauty in their respective styles, and was great fun to play with.

For a refreshing, tongue-in-cheek retelling of Shakespeare's Hamlet, I recommend "To Be Or Not To Be: That Is The Adventure by Ryan North"

Ryan North of dinosaur comics fame?? Oh man, I'll check it out, thanks.

The sequel, Romeo and/or Juliet, is fun as well.

Any of Sherwin Tija's books are humorous, well-illustrated takes on the genres that are definitely not for kids. Plus most of them feature cats! (The original is "You Are a Cat")

https://www.amazon.com/s/ref=dp_byline_sr_book_1?ie=UTF8&tex...

Fighting fantasy books by Steve Jackson. More teen than adult but a significant step up from classic CYOA.

Can You Survive the Zombie Apocalypse? by Max Brallier is the only one I've gone through and it was quite good.