The GNU Project
For all they do for the free community.
The Sourceforge project
The largest Open Source development website. This website is hosting the DeSniff Project.
The tcpdump project
The web site of the tcpdump project and libpcap. Go there to get the last libpcap version.
The libnet's web site
The web site of the libnet developpers.
The DeSniff Project details on Sourceforge
All the informations you need to know is there.