Segue is a little known gem. It is a PHP based LMS built at Middlebury College and used in many others. It offers a host of the standard course features you'd expect but is much more flexible than any other I've seen. In particular I like the web 2.0 models of built in blogging and tagging as standard. There is also a wide selection of templates to allow non-programmers to change the entire look and feel of their site from a simple blog tool to a full blown Course Management System.
You can try the hosted version at Education Commons or go directly to the project website.
The Segue team built the first PHP OKI OSID implementation in project Harmoni which is what is used in Segue to access Digital Repositories.
In todays OKI webcast we kicked off the cross language Java / PHP OKI effort to investigate the XML-RPC bindings. Initially the scope of the project is to develop a proof of concept for existing consumers and providers using a mix of Java and PHP. The list so far includes:

• VUE II
• Segue
• Moodle
• Harvest Road Hive

Project plans and this weeks meeting podcast soon to be posted on Education Commons.