MP4tools is an offshoot of the current version of the popular conversion tools called MKVtools. It is an OS X application used for the creation and editing of MP4 videos. It was primarily designed for processing videos files for use in

AVItools is the part of the VIDEOtoolbox Suite of Applications used for the creation and editing of AVI videos. It was primarily designed for processing videos files for use in DivX enabled DVD players, though the AVI videos it creates

MKVtools is a collection of tools used to manipulate video files. It's primary purpose is to convert mkv files into more user friendly formats for playback on a variety of hardware.