We are happy to announce that you can now run open source projects on travis-ci.com. At the moment you can only add and activate repositories which haven't been tested on travis-ci.org. We are hard at work to add a way for you to migrate your projects from travis-ci.org to travis-ci.com, and should have more information to share on this soon.
If you have any questions I would be happy to help answer them here, or you can email our team at support@travis-ci.com