Mods that give the player a distinctly unfair advantage over others are strictly prohibited! For our server, we consider a "distanctly unfair advantage" to be anything far beyond the mechanics of the original game, such as special clients with various "hacks" that could give a player op status, fly without authorization, enter unauthorized game modes, and so on.
For our server, acceptable mods can include those that improve performance, and lightly tweaks gameplay. If it's reasonably possible to re-create a mod's functionality in the base gameplay, it's probably going to be alright! This typically includes things that re-creates the debug display, numerical display of a weapon's durability, etc as this content is accessible in the vanilla game. We're also fine with expanding this to minimap/health display mods as well.
This is a list of mods that some of our members use! Feel free to suggest ones to add to this list!