hmmm just use linux, then you have a wide range of choies, though bash seems to be the most popular now a days, i grew up with the bourne shell and then used the korn shell which i prefure.

As for windows, well i've played around with linux shells and end up not using them. get worried about all these other shells due to stability issues.

but are you talking about a command shell or are you talking about a tool to change the entire gui interface?