No eroge novels (aka 'erotic visual novels') in this list: there are so many of them that we have made a page just for them.
We also have a page for Adult interactive Fiction for smut made by non-Japanese writers.
Original name is かりんとあそぼ！, also remember to set your PC on Japanese Uni-Code. Very good gameplay, with collectible skills and weapons and some very hard jumps.
The game is in English, but there's no text apart from the start screen and the in-game menu.
It should be noted that as of now, many foreign countries have been IP blocked and none of the online functions will work at all.
You will need a VPN if you want to play online (which is really the point of the game) Lastly, it does not follow regular installation methods.
Awesome graphic and voices for a simple "choose the scene" game where this young woman (who is over 18) does things with a guy she calls her "brother" but they aren't actually related because incest is wrong, Mmmmkay.
Genre feels like a fusion between an original simulator and an adventure game.
Porn is average, but the personal narrative & player agency is stellar.
Different artists worked on the visual art, so they're not all so awesome; not like a leech-girl could look better anyway.
There is also a worthy sequel, and the finale released.