The homepage of a distributed search engine project. The project involves downloading and running a cross-platform spider (available for Windows, Linux, FreeBSD, MacOSX, and pretty much any OS which can run Mono) that will then crawl the web and upload what it finds to the project. This can use lots of bandwidth so consider carefully before joining in.
A distributed version control system, similar to Git or Mercurial, only it also includes a bugtracker, a wiki, and a blog for collaboration in the same package. Includes a web interface for everything. Can automatically sync with other instances. Self contained.
memcached is a distributed database based upon the principle of a hash table: Ask if an arbitrary key exists, and if it does you get the matching value stored in the hash table. If it doesn't, it will be. Least recently used objects get purged from the table to reclaim memory. memcached instances connect to one another so the hash table can span arbitrary numbers of nodes on a network but be queried with a single line of code. Note that securing your memcached grid is your job: It's designed to be run on a trusted network (i.e., your production network that you've hardened behind a firewall that you manage...)
A distributed relational database that uses SQLite as its back end. Eventual consensus of all nodes that relies upon quorum. Automatically elects leaders in the network of servers. More lightweight than MySQL or Postgres. Has a REST API built in. Fully transactional. Hot backups possible. Uses SQLite in "all in memory" mode by default for efficiency, but can maintain on-disk database files with a command line option (the on-disk transaction log can be used to repopulate the in-memory database on startup). Written in Go.
A grid computing project to help find new anti-malarial drugs. Download, install, and crunch numbers in your spare time to help save lives.
A web application for archiving, indexing, and managing your online media content, such as your photo albums, videos, and artwork. Aims to replace Flickr, DeviantArt, Smugmug, Picasa, YouTube, and the like because you will have control over your content and thus be resistant to censorship (plus if they go down your stuff will still be available).
A protocol for transferring encrypted JSON traffic over pretty much anything, from TCP to IRC to sneakernet. Implemented in Python.
Asyncoro is a Python framework for writing massively distributed applications. Designed to work in an asynchronous fashion (including non-blocking network socket handling) on as many OSes as possible. Supports SSL, locking, execution of routines on remote systems, and hot-swapping of code. Even does asynchronous database access.
A curated list of awesome tools and software for sysadmins.