Whelkmud is a windows client that has some extra support for dealing with extra mxp tags. These tags are designed to make the life of the server writter easier and allow much better control on the client side of the information coming from the server to the client.

Currently to get this client to work you will need to download the beta version of .net framework from the microsoft site at Microsoft beta 1 redistributable package. That link will take you to a download set of links, you want the redistributable package and not the sdk, although currently they both appear to be around the same size. In the future one should be smaller, due to less debug information.