Gruntace, Romhacks are usually classed as mods, though obviously many aren't about gameplay.

I've played a modded game of VII right though, gjoerulv's Hardcore Mod (can't remember his name exactly), and I've just started a game of the Brave New World for VI. Whelk withdraw into his shell faster than I was anticipating and I had already given an attack command, so he one-shotted the party. It was fun! There's a VII mod called New Threat (or more commonly just NT) that a lot of people seem to like, so I think I'll go to that next.