It seems like a nice project. I like that you don't need to know a particular programming language to use it.

The way you define services feels a bit awkward though.

Also, it seems like install.sh scripts for various platforms would lower the barrier to entry. The installation documentation is nice enough, but really that should all just be scripted so it can be condensed to:

curl http://cast-project.org/install.sh | sh

Running runit scripts out of a user home-dir (as in the example) does feel wrong to me though.