Jay Dolan from Quake2World has been developing a version of Radiant that can run in a web browser...
http://radiantjs.com/
The real benefits in mind seem to be multi-platform support and the ability for multiple map designers to work on a map simultaneously. It should be pretty interesting to see how this pans out.
Radiant in your browser
Re: Radiant in your browser
Yup, periodic discussions of this on the #radiant IRC channel
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