.LRN – a free software educational content management system based on the OpenACS platform. Quite difficult to get installed (a task that I have not yet managed to complete).
Moodle – an open source educational content management system written in PHP.
Rhaptos – an open source educational content management system based on Plone (which, in turn, is based on the Zope application server). Uses MathML and supports a number of browser plugins for advanced features.
OCW – MIT use a system based on Microsoft Content Management Server. (See: 1 and 2).
UCalgary have a learning object repository.
Heriot Watt University, Cranfield University and the University of Birmingham collaborate on EEVL, “the Internet Guide to Engineering, Mathematics and Computing”.
Chalkface are publishers of online courses, lesson plans, photocopy masters, etc. for secondary education in a wide range of subjects.