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.
Playtomic is a set of client and server APIs for game leaderboards, user generated content, and dynamic updates. It began as a hosted service providing tools and analytics for game developers, but is now available for developers to operate on their own. It includes the API server which is written in NodeJS and backed with MongoDB, along with game client APIs for HTML5, Flash, iOS, Android, Windows, and Unity3d games.
PerlShare is a DropBox drop-in to create your own private file sharing "cloud". It consists of two parts; a client and a server. The server part lets you configure a Linux machine to accept PerlShare clients. PerlShare behaves a lot like DropBox. On collisions, for example, it creates conflicted copies. The workhorse for synchronization is Unison, a very reliable piece of software from Pascal Bach.
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.