Our number one commitment is to an exquisite personal computing environment. Imagine a system as immediate and tactile as a sketch pad, in which you can effortlessly mingle writing, drawing, painting, and all the structured leverage of computer science. - Dan Ingalls, Squeak's Place in the Universe
You can run Squeak on handhelds and other pen-based systems. Why, you may ask? Read and add to What I use handheld Squeak for.
Pens v. Mice Notes on some differences, from a UI viewpoint, between pens and mice.
Ready to use Images and Environments
Dynapad: (Dec 2008 - Link points to non-Squeak stuff.) An operating environment for PDAs, written entirely in Squeak. Small (5 MB) image with features to make using Squeak on such a device worthwhile. Also with standard PDA software, including games and a PIM.
The KernelImage provides (as of 3.9) images built up from core modules rather than stripped, which can load Monticello and other packages to grow into the set of functionality needed.
Spoon images may also be suitable (although the Flow VM plugin must also be ported; granted, that is very easy).