GNU libmicrohttpd is a small C library for embedding HTTP server functionality into other applications. It is reentrant, fast, supports HTTP 1.1, and permits listening on multiple ports. The API is simple and still powerful enough to allow programmers to use the entire HTTP feature set. SSL/TLS support is available as an option.
MojoMojo is a Web2.0 wiki with AJAX live preview, hierarchical structure, tags, diffs, pluggable syntax, permissions/ACL, attachments, RSS feeds, a photo gallery, edit conflict resolution via 3-way merge, themes/skinning, localization, built-in full-text search, and a reverse index. Since it's built on top of the Perl Catalyst Web framework, MojoMojo supports any Web server, and includes its own standalone one. It also support any database backend supported by the DBIx::Class ORM, and has been successfully tested with PostgreSQL, SQLite, and MySQL.
fakedbfs is a suite of tools and a library for cataloguing files. Anything that is a file can be catalogued along with metadata. The metadata is then searchable through various querying facilities. It runs entirely in userland and was inspired by BFS, which doesn't do content indexing, only metadata.
Octaspire Crates! is a scriptable, skinnable, extensible, and relocatable 3D action puzzle game. All the missions, game entities (or crates), game states, and configuration of the game engine are implemented as plain text Lua-scripts. So, if you know Lua, you can write new game entities, game states, missions, and levels with any text editor, without any special development tools. New skins can be created with any image editor that can save .png images, dropped into a new subdirectory under the resources/textures directory, and changed in the configuration file config.lua. Crates has also its own (simple) implementations for all the different container classes it needs (like vector, string, and so on) to keep the external dependencies fewer.