JRE is required to run the program (even if it's exe-wrapped), get it here:
http://www.java.com/en/download/manual.jsp

 

Mencoder is used for actual joining, it is a part of mplayer and can be downloaded at http://www.mplayerhq.hu/design7/dload.html
It is free and distributed under GPL.

 

mJoiner Sourceforge download page:
http://sourceforge.net/project/platformdownload.php?group_id=238280
(exe-wrapped version is recommended)

 

 

Mencoder GUI frontend, written by Pivovy for reasons better left unsaid. Also check out Daffpix - udaff.com picture viewer.