RailsMan is still in very early development stages. It seems to work, at least on my machine, most of the time! It's quite possible that if you're doing something out of the ordinary (e.g. using a different ruby or rails stack than the default Leopard one) that it just won't work at all. Please give me feedback if you run into troubles! I'll do the best I can to get it working on as wide a variety of setups as possible.
RailsMan is released under the GPLv2 licence. It is free to use, and source code is available from Sourceforge.net.
If you would like to support the development of RailsMan, you may do so by donating. Probably more importantly, though, you can get involved in the development. Drop me an email if you would like to help out.