The Limb framework project (up to its limb3-2007.4 release as of this post) is an Open Source PHP framework that looks to help developers create applications quickly and simply.
We are committed proponents of the beautiful and easy-to-maintain code that simply works. That is why we develop and constantly refactor the Limb code in a test driven manner using the best agile development practices.
There's different ways to get the latest version of the framework - either from their PEAR channel or from a direct download of the entire package. Currently, the framework is made up of a grouping of components that do things like input filtering, make MVC setups simple, allow for active record implementations and an included tests runner.
You can get complete information on Limb-Project.com (including some documentation, information about the Subversion repository and links to community resources).