Pharo Open Source Smalltalk. I should take another look at it, as it looks very sleek now and the installation has become really trivial. Clever how a Pharo.App directory is loaded, which is the app for OSX and includes simple startup tools (LNK for Windows and .sh for Linux) for Linux and Windows. Additionally, there is a new VM and the whole thing has become really fast. And it no longer looks so outdated (unfortunately still GUI-in-window and no native windows).