Shadertoy shaders works almost as is in current Leadwerks 3.0, but you just need to rename iChannel0 to texture0, iTime to currenttime etc..
However shadertoy is mostly built for showoff and uses fullscreen texture coordinates.
Here is a shot of the moving clouds from shadertoy in a LE3 scene :
There is no visual designer, but there is a glsl editor and a material editor.