Multiplatform. Runs on a virtual machine. Virtual machine for 32bit Squeak 4.6/5.0 runs on Windows, Linux, Mac. Virtual machine for 32bit Squeak 4.6 also runs on FreeBSD. If you develop something you can not live without you can take it with you to Windows, Linux, Mac (Squeak 5.0) and even FreeBSD (Squeak 4.6).