Underwater Rails by Hennamann
Made for Modjam 5 adds 2 new rail types and tools intended for use underwater.
Underwater Utilities by Shadowfacts
Helpful utilities for working underwater.
Undestructible by The_Icy_One
Make your structures undestructible.
Unfathomed Depths Mod by Josh029
Ancient Technology of Mysterious Depth.
Ungrab Mouse Mod by Jaideep Singh Heer
This is a simple mod to allow players to ungrab the mouse to do other things on their PCs while the game runs.
Ungui by Mrkol
Declaring a war on GUI screens! This was made as part of MODJAM3. If you are reading this in 2014, then I probably got into top 10. Otherwise I would totally be all sad and stop modding for a couple more months :(
UniDict by WanionCane
a mod about unifying all the things.
UniQ by domi1819
OreDict unifier
Unicode Font Extension by BRE
This mod allow you to read very small unicode fonts.
UnicodeFontFixer by oldjunyi
UnicornMod by SquidBananas
This is a Mod that adds Unicorns and a new Biom!!!
Unidye by LinusPhoenix
Makes Wool Dying and Dye obtaining much more convenient. Needs IC2.
Unified Items
Adds items and blocks like copper and tin so that we can have a more 'unified' playing experience
Unified Items by chazwarp923
Adds items and blocks like copper and tin so that we can have a more 'unified' playing experience
Unified Mode for In-game Account Switcher by The_Fireplace
The Unified Mode addon for In-Game Account Switcher