Something that occured my mind when browsing the list is that Lix packs are completely absent. I think it would make sense to have Lix level packs in their own category, here are links:
Clam
ClamLix (currently a work-in-progress)
TameLix (ONML Tame levels in Lix with new puzzles, easy and hard puzzles for each level)
Dodochacalo
DoveLix (DoveLems, originally a pack for Lemmini, facilitated by Proxima. This pack also needs separate Lemmings tilesets, that don't come with the Lix game.)
mobius
mobius' lix level sets (levels converted from Lemmix, some of them are in the Lix community pack)
Nepster
NepsterLixProb Lem
Prob Lem's Lix LevelsRaymanni
RaylevelsRubix
Epic AdventureLost (15 levels from Epic Adventure with different skillsets)
Reloaded (original Lemmings levels in Lix with new puzzles)
Time trialsThe Lemmings Community
Project Capybara (I guess discontinued (?), facilitated by möbius)
The Collab Lix puzzleAnd then there's that not yet completed Lix community level set that has so many "in development" topics..

By the way, Lemmings Migration is under Nepster at the moment, "Nessy" is missing from between.