Turns out there are like 40+ plugins and I can't find any documentation ever since he left GitHub, so here are some of his killer apps I know of.
- JetPack is just the API his other plugins are based on. Think of it like KKAPI or Harmony. Does nothing visible on its own, still important that it's here.
- WhateverTheFuck converts a clothing item into an accessory. It released at a time when Clothes to Accessories, the HF patch equivalent, was broken and probably drove a lot of conversion. C2A was fixed a while ago and WTFix was developed to convert WTF data into C2A data.
- AccStateSync allows you to toggle the visibility of an accessory and its renderers based on clothing state. Powerful stuff when combined with WTF, since this means you can force the full state of a Top to show even when top is set to half-off or so. AccStates and ANAL on the HF side have mostly replicated this, but only for the entire accessory and not individual renderers.
- BonerStateSync allows tweaking ABMX data based on current coordinate and clothing state. Mostly used for high heels, though you can also do something like having a big and smol version of the same character in the same coordinate if you want. The HF equivalent of Stiletto is still a bit broken at times, so there remains a legitimate use case for this one. ManlyMacro did speak of implementing this in ABMX itself though.
- HemorrhoidsBuster batch moves accessories in the same coordinate and MoveUrAcc batch copies/deletes/compresses accessories between coordinates. Both have since been replicated by AccMover.
For some honourable mentions I know but don't consider to be terribly important:
- CharacterAccessory allows you to mark certain accessories so they don't get overwritten when a new coordinate is loaded. Used to preserve hair accessories when you want to play around with coordinates, but just copying them over and preparing new coordinates before playing in Studio is only tedious, not impossible.
- CreamAssWipe resolves backwards compatiability between Creamstar's hair mods, since Creamstar switched the internal IDs of some hair items around on update and may cause older character cards to break. I understand the use case for that, but naming your plugin like that is just such a dick move, especially coming from a prick like Madevil. I'd like for WTFix to be renamed UpMadevilsAss but that is just giving underserving people publicity.
- MaterialRouter seems like it may be important but I genuinely have no idea what it does or how it works. If only someone would release and document it on GitHub like a functioning member of society.
As for KKS, I am not familiar with the nitty-gritty of plugin development. Based on what I can find it seems you have to specifically compile for KKS and maybe tweak your code based on subtle differences between the two games. Madevil simply never bothered to do so.
All in all, Madevil used to offer some really important plugins that go beyond just QoL and drew in a lot of users (his plugins are still popular in the Chinese community because their repack uses them). But HF has caught up since then. It's almost like the ecosystem develops faster benefitting everyone when you actually embrace FOSS development and collaborate with other developers instead of sulking in your cave like a manchild.