Ask HN: Is there anything specifically you've done to get co-contributors?

For those of you who have started open source projects, is there a specific course of action that you remember as being effective in getting other contributors on your project? I can think of lots of things to try, but I don't know if any are actually effective. Among them I can think of: * Documentation targeted at developers * Guidelines for contribution * Permissive licensing * Automated builds and testing * Other? I can come up with arguments why all of these might help. However, since time is always hard to come by, it'd be interesting to know what people have tried and what actually works.