Video Projection Tool (VPT) is a free multipurpose realtime projection software tool for Mac and Windows. VPT 7 was downloaded over 100000 times, so in spite of a lot of other options available VPT still is popular.

Among other things it can be used for projecting mapping on complex forms, adapt a projection to a particular space/surface, combine recorded and live footage, for multiscreen HD playback, for interactive installations using arduino sensors or camera tracking ++. VPT is very flexible in terms of control, with presets and a built in cue list, as well as control over almost every single parameter using OSC, midi, serial communication, built in LFOs and ArtNet. It also supports syphon (mac) and spout (windows) for sharing video streams between applications.