WorldStateCheckpoints is a client mod that allows you to create world saves for your SP worlds.
clientside opensource backup
Wormholes by armaDio, GabrieleMaurina
Have you ever wondered what happened if you went through a wormhole in minecraft?
Wtfmod by YeaTouh, MCreator, YeaYouh
A mod with some weapons, mobs, and a dimension [ MOD IS IN BETA ]