I think it would be fair to call Dimdim a WebEx "mee-too" application.

Dimdom offers a web- and Flash-based meeting application which allows you to communicate (via video, audio or text) and to collaborate through whiteboards. You're able to share a presentation or even you whole desktop (at least if you're still on Mac or Windows).

The most outstanding feature however is the released source-code. Not only open, but also free as in speech, distributed under the terms of the GPL.

Even if you're not interested in deploying your own server, you might want to trade any other web meeting portal for dimdim. Unfortunately, sharing your Desktop with Linux is not possible right now, but at least it's on the roadmap.

While I consider the release of the source code a really smart move of Dimdim Inc., I wonder why they don't offer paid support for the open-source edition. There are a lot of companies who prefer FOSS, but still able and willing to pay for their software through support contracts.