The announce from SilverStripe Core Development that all modules marked as Silverstripe supported, have been moved from svn to GitHub.
Modules were previously hosted on svn.silverstripe.org and are now hosted at https://github.com/silverstripe . This doesn't include the Silverstripe "core" though (phpinstaller, sapphire, cms) which will be migrated over the next days/weeks.
Other modules available at svn.silverstripe.org will progressively be migrated to their owners' github account when possible, or other places such as Google code.
For people using svn:externals to the trunk, the core team suggest to use Piston, which copies a snapshot of the code into your own repository and knows how to update this snapshot. For people using a specific tag instead, the SVN repository is still available (read only).
Downloads at http://silverstripe.org/modules will continue to be available.
Previous SVN repositories are now read only and contributions will be managed via pull requests (see http://help.github.com/pull-requests for a good tutorial).