Yintersync uses the following excellent open source tools.

Rsync http://rsync.samba.org/

NSSM http://iain.cx/src/nssm/ - No longer used as of version 0.6.0b
SSHPass http://sourceforge.net/projects/sshpass/ (The source code for modifications as per the GPL is here, details are here)
Cygwin http://www.cygwin.com/ (Modified the source for cygrunsrv.exe, this is availiable as per the GPL here, details are here)
OpenSSH http://www.openssh.com/