OSgrid is the largest running OpenSimulator grid, we are officially non-profit, and it is completely free to connect your own regions to the grid. You can get started by registering an account and downloading a viewer.
Sloodle en Osgrid from Raul Mojica on Vimeo.
SLOODLE is an Open Source project which integrates the multi-user virtual environment of Second Life with the Moodle learning-management system.
SLOODLE provides a range of tools for supporting learning and teaching to the immersive virtual world; tools which are integrated with a tried and tested leading web-based learning management system