Well... From what I gather, "Doujin games" aren't usually fanworks - the name just refers to computer games which (like their comic counterparts) are created by non-professionals (and not always for profit). A lot of them are of the "dating sim" variety, and many of the most famous (infamous?) of them are very male-oriented and pornographic in nature. The ones I mentioned in my first post are doujin games, and both of them are distributed freely.... But they're not porn.
"Visual novel" (aka "kinetic novel", apparently...) is sort of a sub-category, referring to doujin games (or professionally-produced games, for that matter) that don't have an interactive component. Like I was saying, they *do* read very much like webcomics, or any other comic, for that matter. You're presented with static images, below which is the text of the "novel". You read it, the images change periodically, and hopefully, you are moved by the story.
Really, there are only 2 main differences between a visual novel and a webcomic: (1)There is usually accompanying music, and (2)The ratio of text to images is much higher. In the webcomicking field, we usually try to "show and not tell", whereas in a visual novel, there's a helluva lot of stuff to read. I suppose the amount of action would depend on the novel in question, but the above two didn't contain much of any action - or, if they did, it was all presented via text. In fact, the images in both were *very* sparse; I suppose, like real novels, they try to get you to use your imagination. (P.S. - play the "unvoiced" version of Narcissu if you try it out; it really is better when you can imagine the girl's voice.)
So, uh... Yeah.
Oh, apparently "Planetarian" isn't 18+ either... But it's also not free, and in spite of its non-porn status, it looks like something geared towards males anyway...