Second Life. The MMORPG. Was a fun community to start. Not sure if its still around. As far as a VN type has to be Superpowered or The Tyrant. Those are the first that I remember enjoying and maybe the first Bad Bobby.
it was loooooooooooooong time ago so i don't remember which one was first i played.
Edit: Not true, there was one game on PS1 i played when i was a kid, you had to find difference between 2 pictures of naked lady, another thing i remember is when you beat the game adult cartoon played, witch (she had teeth in her vagina) had sex with a knight if i remember correctly after the sex she ate him, to be more precise her vagina swallowed him.
Really depends on the timeline here. I grew up during the golden age of Newgrounds. That's where I got my first exposure to adult gaming. If we're talking silver age here, then it would have to be Big Brother or Dream of Desire. I played some bangers back in the day, but those two would have to be my stand out examples.