Myself and a buddy are creating http://sidekicks.io, a platform which allows developers and designers to work with each other on various projects, and in return they gain "karma" to use for work on their own projects that need contributors.
We are accepting sign-ups now and have been able to get some great interest. We will launch the full platform in a few weeks.
Some of our early sign-ups have asked to help build the platform, so they are helping us build it.
If you are interested in contributing let me know!