Beta 1 of WordPress 2.6 has been released! If you want to test it safely, you should be able to do so as soon as the WordPress 2.6 demo site is updated.
Update: Robert posted a comment pointing out an alternate demo site.
WordPress 2.6 was previously slated for an August 2008 release, but the WordPress Trac Roadmap has recently been updated with the following information on the WordPress 2.6 release date:
Originally published on April 24, 2008. Updated on May 5, 20, 22, June 16, and June 20.
WordPress 2.6 may not be due until August 2008, but already I’ve managed to compile a list of features and enhancements that we’ll likely be seeing in this next major WordPress release. (I’ll continue to update this post as we approach the release date.)
As reported in my updated WordPress 2.6 features list, support for Google Gears in the administrative back-end has been added to the WordPress Trunk (i.e. the current development version).
According to the development ticket for the Google Gears patch: