Squeak/Pharo, a practical Smalltalk written in itself

at Apple Computer while doing this work, now at

Squeak is an open, highly-portable Smalltalk implementation whose virtual machine is written entirely in Smalltalk, making it easy to debug, analyze, and change. Originally developed on the Macintosh, members of its user community have since ported it to numerous platforms including Windows 95 and NT, Windows CE, all common flavors of UNIX, and the Acorn. Therefore our ideal system would be a small, portable kernel of simple and uniform design that could be adapted rapidly to new delivery vehicles.

Source: ftp.squeak.org