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-2.1.2-win32u.exe (7.7 MB)
Mac OS X binary: MP4Joiner-2.1.2-MacOSX.zip (20.2 MB) - unpack it to start
Source Code: MP4Joiner-2.1.2.tar.bz2 (171 KB)
Portable Application Description: pad.xml, pad-osx.xml