Chris Corbyn was frustrated with PHP's lack of a good REPL, so he took matters into his own hands and created Boris. I can relate to Chris's experience. Back when I used to write WordPress plugins I got so frustrated by the lack of a Rails-like interactive console that I created one for WordPress.
Boris is cooler than my little plugin because it works outside of WordPress and runs directly in your terminal. Check it out in action:
You can install Boris via Packagist or use it directly by cloning the repo:
git clone git://github.com/d11wtq/boris.git cd boris ./bin/boris