Editors

Booster's Lab
by Noxid

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)
Forum Thread  

Cave Editor
by Wistil

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
Source Code
Forum Thread  

Ikachan Map Editor
by gamemanj

A map and npc editor for Ikachan.
Ikachan Map Editor v13.1
Forum Thread