None of the Telerik products is open source. We offer two versions of RadEditor for MOSS. The Lite Edition which you have already downloaded is available complimentary to all registered clients of Microsoft SharePoint 2007. The RadEditor Full Featured MOSS Edition is available as part of the RadControls for ASP.NET AJAX suite. You can review the detailed comparison between the two editor editions here:
If you are interested in purchasing the RadControls for ASP.NET AJAX suite (which includes the RadEditor Full Featured MOSS Edition), you can opt for the Developer License, list price $799 or the Developer Subscription and Source Code License, list price $999. The latter is our value added proposition, which entitles you to a Gold Support Package, free product updates and new product releases for a period of one year. The RadControls for ASP.NET AJAX licenses are available for purchase from here: www.telerik.com/Purchase.
If there is anything else I can assist you with, please let me know.
the Telerik team
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