Display only part of layer/animate squence of layer printing
Analyze GCode
Print time, amount of plastic used, layer height, etc. for whole file and for single layer
Reference visualized part to GCode file (i.e. select a certain part of 2d visalization, switch to GCode view - it will highlight list of lines responsible for visualized piece)
Multiplatform, available online (but works offline too), works locally (doesn't upload you gcode anywhere or download anything but application itself)
3D visualization (I don't know what for, it's dull and useless.. need to rewrite it to be like in repetier host)
And yeah, it's slow, memory hungry and only supports modern browsers like chrome and ff of latests versions (maybe safari 6 and ie10, haven't checked)
Totaly open source so you can use it as you like )