GMime is a C/C++ library for parsing and creating messages using the Multipurpose Internet Mail Extension (MIME).
The GNU Privacy Assistant is a graphical frontend to GnuPG and may be used to manage the keys and encrypt/decrypt/sign/check files. It is much like Seahorse.
An IDE for HTML, Bash, Perl, PHP, C, etc.
A ClamAV antivirus redirector for Squid.