OPT (Outreach Project Tool) is a PHP general-purpose virtual commonplace for customers and developers to collaborate in developing projects. The system provides documents archive, e-mail archive, request tracker, task management, knowledge base, news administration, newsletter support, and a lot of other features (some project-based, some system-based).
pDonkeyS is Perl implementation of an eDonkey server. The main goal of the server is to provide framework for further eDonkey protocol exploration, but it could be useful in testing of client software, since the server can be configured to output very detailed debugging info about eDonkey traffic.
MetalServe is a standalone DCC file server that can be used to share files on Internet Relay Chat (IRC) networks such as EFNet and Undernet. Unlike the only available similar Unix program, iroffer, which offers "packs" of files, MetalServe offers single files similar to the way the SDFind, SPRJukebox, and OmenServe scripts for mIRC, a Windows IRC client, work.
FileNabber is a Java servlet packaged as a Web app (WAR file) that allows you to download (via HTTP or FTP) remote files to the server and upload remote files to the server via HTTP. It has a progress bar for uploads and downloads, and also supports themes to make it easy to customize the look of the pages. It runs on any servlet engine that supports WAR files.