Pre-releases are available for the desktop application. They are pretty much like regular releases, except that they have not yet been tested by many users, so it is possible that a bug or two went through.
In general it is safe to use these pre-releases (they do not include any experimental or unstable features). In fact most pre-release eventually become regular releases after a few days.
To have access to these pre-releases, simply go to Configuration screen and tick the box "Also get pre-releases when checking for updates".