mpssh and kash are also good. kash is part of the kanif perl project, but the one thing about it I really like that I don't see other projects doing is that it will aggregate similar output before it spits it back.
Thus if you run it to check for a package version on 300 servers, you can get maybe 2-3 sets of output grouped by host based on the output vs 300 lines of output.
Thus if you run it to check for a package version on 300 servers, you can get maybe 2-3 sets of output grouped by host based on the output vs 300 lines of output.
https://github.com/ndenev/mpssh
http://taktuk.gforge.inria.fr/kanif/