An actively updated in-development editor written in Java. It can be used to create both CS and CS+ mods.
Booster's Lab v0.4.1.4 (English)
Booster's Lab v0.3.3.0 (Japanese)
Has a number of features not present in Booster's Lab. Both editors are compatible with each other so it's down to personal preference as to which interface you prefer.
Cave Editor v0.99d