Yes.
For Macintosh hosts and guests GatherPlace has a native client that can be downloaded for free here or they can use any Java enabled web browser running Java 1.3 or higher.

Linux hosts or guests that need to share their screen or use any of the advanced features in a meeting must use a Java enabled web browser running Java 1.3 or higher (no native client is available for Linux).
Linux guests that do not have a Java enabled web browser can also join a GatherPlace meeting from any graphics enabled web browser using the SureView viewer.

Note that SureView is strictly a viewer and guests joining using this method will only be able to see the presentation. They will have no advanced features available in the meeting.
For more information on SureView, please see this article.