The Force
Open source, live coding editor for WebGL
5 Alternatives To The Force
KodeLife
Real-time GPU shader editor, live-code performance tool and graphics prototyping sketchpad.
SHADERed
Lightweight, full-featured desktop tool for creating and testing HLSL and GLSL shaders
ShaderLab
WebGL2 GLSL Editor for the browser.
ShaderWorkshop
Qt based, interactive GLSL fragment shader editor
Shaderific
Create shaders on the go with the OpenGL shader development app for iOS