is an open source PaaS built on Docker
. A PaaS is like Heroku, but an open source one allows you to run it anywhere, even on your cheap VPS, which not only greatly reduces costs but also avoids vendor lock-in. It'll even support Heroku buildpacks so that you can run Ruby, or whatever Heroku already supports. Flynn is in an early stage of development and its authors are seeking funding so that they can concentrate on the project full time.
Docker is a Linux container system. Compared to regular VMs, Docker containers are much more lightweight. You don't have to allocate a static amount of RAM. The RAM is shared with the host OS - everything runs on the same kernel. This saves tons of money and hardware resources.
The Flynn authors state that even if they don't reach the funding goal, they will work on Flynn, but it will take much longer and the end result won't be as polished.
So if you can spare some money, please consider supporting Flynn!