http://www.atutor.ca/acollab/index.php
If you weren’t already impressed enough with Atutor, the accessible, open source LMS from U of Toronto’s Adaptive Technology Resource Centre, along comes the second piece in their ever-growing suite of accessible learning technologies. With shared document authoring, calendering, chat, threaded discussion and extensive group support, ACollab is WCAG 1.0, Section 508 US-compliant software that can be easily integrated with Atutor to provide a powerful open source learning environment. Caution: use of this product may actually enable learning amongst an entire class of people who are otherwise discriminated against by badly designed, inaccessible technologies. – SWL