Modul8 is described as 'VJ is a revolutionary MacOS X application designed for real time video mixing and compositing. It has been designed for VJ and live performers'. There are more than 10 alternatives to Modul8 for Windows, Mac and Linux. The best alternative is Vidiot, which is both free and Open Source. Other great apps like Modul8 are Resolume Avenue (Paid), Isadora (Paid), LiVES (Free, Open Source) and VDMX (Paid).
LiVES is a Video Editing System. It is designed to be simple to use, yet powerful. It is small in size, yet it has many advanced features. LiVES mixes realtime video performance and non-linear editing in one application.
VDMX5 was created from the ground up to meet the demands of realtime video performance. Built around a robust data processing architecture it was designed to be used with whatever hardware- or software- you've got available.
vMix is a Software Video Mixer and Switcher that utilises the latest advances in computer hardware to provide live HD video mixing, a task previously only possible on expensive dedicated hardware mixers.