Digg competitor Mixx just launched an extension to its groups feature that founder Chris McGill describes as “Ning for social media”.

Users can now set up Mixx community sites on their own subdomains (see ours here). Administrators have the power to brand them visually, post editorial content, and even make some revenue off advertisements. Others can join as members and begin submitting items as they would regularly on Mixx. All submissions (stories, images, and videos) can be made just to a particular community, or to the Mixx site as a whole as well.

This release is more akin to Reddit’s hosted “create a Reddit” service than it is to Reddit’s new open source offering since Mixx communities are hosted and can only be rebranded to a limited extent (with custom logos and color schemes).

Just as the standard Mixx experience is divided into verticals like Entertainment, Science and Sports, communities can deploy their own tabs for niche topics. The TechCrunch community, for example, has been seeded with tabs for “Obtaining Funding”, “Creating the Dream Team”, and