Booster's Lab
by Noxid

An actively updated in-development editor written in Java. It is the most feature-rich of the two editors and can be used to create both CS and CS+ mods. Booster's Lab v0.5.1.1 (English) Booster's Lab v0.5.1.1 packaged with JRE (English) Booster's Lab v0.3.3.0 (Japanese) Forum Thread   Github  

Cave Editor
by Wistil

No longer actively updated, but it still holds up well when compared to 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 v15.2 Ikachan Map Editor v13.1 Forum Thread  

Kero Hack Tools
by JMickle

A map editor for Kero Blaster and Pink Hour. It isn't all that user friendly so check out the usage instructions link below before you use it. KeroHackTools v1.2 Usage instructions Forum Thread  

All-Seeing Eye
by Brayconn

An editor for Guxt. All-Seeing Eye v1.1.1 Github Page