https://github.com/Spakman/urchin/
I really like a lot about existing shells like Bash and Zsh, so it operates much like a standard shell - pipelines, job control, redirections, tilde expansion, aliasing, globbing, etc.
However, actual shell scripting feels really grim, so sometime in the near future (hopefully) it will be able to pipe into Ruby when needed. This will let you write Ruby directly on the command line, without escaping quotes and such and should make loops and custom shell functions much more fun for a Ruby programmer.
I also fancy experimenting with some things I've not seen in other shells - fuzzy filepath completion, per-project history, etc.
Any ideas are welcome!