The very capable 0.5 stable release has just been released for Windows, Linux, and Mac OSX! Other OSes might work, but we don't know...
This new release includes new features such as:
* Avatars
* Game distribution
* Easier to use Lua scripting system
* A graphical installer
* A graphical world launcher
If you have any problems, register for an account at http://openblox.sourceforge.net and post in the forums, under "Troubleshooting".
We hope you will like this very powerful and user-friendly release!