Peel's client is a good start of a client, but it is too immature at the moment (feature-wise, not quality-wise) and he appears to have lost interest. (to be fair, I believe Peel has actively sought someone to pick up the torch)
I have been using GGMud and I'm fairly pleased with it. It seems to be tt++ in a gtk window. It runs in linux, MacOSX and Windows... so it's cross platform.
It has one idiosyncrasy I'd like to see if I can get adjusted, it only accepts the four cardinal directions on the number pad for movement. This would be a good litmus test to see how active and receptive the coder is.
http://www.ggsoft.org/ggmud/