Similar to shadertoy.com, glslsandbox.com, and glslb.in. Fragment is a constrained design tool for content creation within the boundaries of two triangles. If none of that made any sense, please visit www.shadertoy.com
Unlike shadertoy, Fragment is a native macOS app, that allows you to edit your GLSL code with which ever text editor you prefer. Fragment allows you to render out high resolution prints, and png sequences (with transparency if you want it)! Also, you can VJ with Fragment by sending it OSC :)
Fragment allows you to create playable real-time visual instruments. It does this by creating UI elements (sliders, buttons, etc) from comments in your glsl code, i.e. uniform float foobar; //slider:0.0,1.0,0.5.