Sanewall is a firewall builder for Linux that uses an elegant language abstracted to just the right level. This makes it powerful and easy to use, audit, and understand. It allows you to create very readable configurations even for complex stateful firewalls. Sanewall can be used for almost any purpose, including control of any number of internal/external/virtual interfaces, control of any combination of routed traffic, setting up DMZ routers and servers, all kinds of NAT, providing strong protection (flooding, spoofing, etc.), transparent caches, source MAC verification, blacklists, and whitelists. Newer versions abstract the differences between IPv4 and IPv6, allowing you to define a common set of rules for both, while permitting specific rules for each as you need. Sanewall is a fork of FireHOL and can make use of existing FireHOL configurations.
NanoHttpd is a lightweight HTTP server designed for embedding in other applications. It's only one Java file, in two "flavors", one strictly Java 1.1 compatible, and one at "current" standards. It supports GET, POST, PUT, HEAD and DELETE requests, and supports file uploading with very small memory overhead. Temp file usage and the threading model are easily customized.
netjukebox is a Web-based media jukebox for MPD, VideoLAN, and Winamp/httpQ. It features realtime MP3 streaming from different audio formats. Users can download single tracks or a whole album in one zip file. It is also possible to batch-transcode the whole music collection to another format or bitrate without touching the original files.
nimsg (the Network Instant MeSsenGer) is a compact, server-based chat program. Its features include the ability to chat with more than one person at the same time, the ability to post multiple times in a row, and the ability to let users choose their in-chat nicknames. It can be used as an alternative for IRC, for those times where you just want to have a small, local chat room.
SyncServer is a Firefox sync server written in Perl. Mozilla's Firefox sync server, which is written in Python, has many dependencies and is quite tricky to install on enterprise distributions which don't ship with all those requirements. This syncserver implements the syncserver user API and storage API as an fcgi application. It is entirely written in Perl.