MP4Joiner is a cross-platform free application that allows join multiple MP4 files into one without reencoding and without quality loss. It is Open Source Software and is completely free.
Windows binary: MP4Joiner-2.0-win32u.exe (7.3 MB)
Mac OS X binary: MP4Joiner-2.0-MacOSX.zip (18 MB) - unpack it to start
Source Code: MP4Joiner-2.0.tar.bz2 (138 KB)
Portable Application Description: pad.xml, pad-osx.xml