KodeLife is described as 'fast, lightweight, live-coding IDE for shader development. It's available natively across Mac, Windows and Linux desktops and supports all flavors of OpenGL GLSL, as well as platform specific shading languages such as the Metal Shading Language and DirectX HLSL' and is a Code Editor in the Development category. There are more than 10 alternatives to KodeLife, not only websites but also apps for a variety of platforms, including Windows, Linux, Self-Hosted solutions and iPhone. The best alternative is Shadertoy, which is free. Other great sites and apps similar to KodeLife are Shader Editor (Free, Open Source), SHADERed (Free, Open Source), Shade - Pro Shader Editor (Freemium) and Shdr (Free, Open Source).
ShaderTool provides a flexible and editable node-powered pipeline that allows you to write shaders without also having to have written an engine. Use the integrated code editor to directly write shader code in either HLSL (DirectX) or GLSL (OpenGL).
Shader Frog lets you create visual effects by composing two or more shaders together, and tweaking their parameters. You can build a complex effect out of simple components. You can then export your shader for use in your THREE.js game or application.