Squeak is an open, highly-portable Smalltalk implementation
whose virtual machine is written entirely in Smalltalk, making it
easy to debug, analyze, and change. To achieve practical
performance, a translator produces an equivalent C program whose
performance is comparable to commercial Smalltalks.
Other noteworthy aspects of Squeak include: a compact object
format that typically requires only a single word of overhead per
object; a simple yet efficient incremental garbage collector for
32-bit direct pointers; efficient bulk-mutation of objects;
extensions of BitBlt to handle color of any depth and
anti-aliased image rotation and scaling; and real-time sound and
music synthesis written entirely in Smalltalk.