A complete wiki distributed as a single self-modifying HTML file. Dripping with Javascript options and tools. You don't need a web server or a database, just a relatively recent web browser and someplace to store the file. Can be freely shared on a web
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.