It runs on various unixes (without wine), it ran on win32 Alpha (another meaning of the word portable) - I'll give you ugly, but its fully functioned, and arguably much easier to use than the command line openssh-client.

Well designed can refer to more than just the interface. It meets historical windows human interface guidelines too.

I'd also suggest that its an open source project, and could be forked, with a new UI wrapped around the existing pretty good terminal emulation.