The best part is that both rkt and actool have been installed in the CoreOS image. I'm not sure exactly when that started but for the time being the latest Alpha (695.0.0) is good enough.
$ rkt versionand
rkt version 0.5.4
appc version 0.5.1+git
$ actool versionBut the challenge for me is that I'm using CoreOS for development too. So while I have a fairly involved setup script I also need to install rkt and actool.
actool version 0.5.1
tar xzvf rkt-v0.5.6.tar.gz
env GOPATH=/root/_vendor/ go get github.com/appc/spec/...The actool installation was pretty tricky because the source did not provide this info.
There is another tool call goaci. This tool is supposed to create aci files from your go project. This did not work for me (as yet) because I have a private project and the repos may not be smart enough to use the keys. Specially since the tool seems to be converting the git commands to use https APIs instead of git which would use the SSL keys.
UPDATE: you have to move the contents of the rkt folder to a bin folder somewhere. In my case since I'm using the CoreOS toolbox I moved the files (rkt & stage1.aci) to the /root/bin folder.