The Pi version of Scratch (based on Squeak Smalltalk) is available for beta testing. Feel free to help moving it forward.
It is not the only implementation: Phratch (based on Pharo Smaltalk) is basically running on the Pi too.
You may ask what are the differences between Scratch and Phratch: if I understood correctly from the discussion on the lists I think the Squeak version now has a paid maintainer (Tim Rowledge) and follows the original Scratch for kids. Phratch from Jannik Laval is more oriented towards a "Scratch for grown ups" and tries to profit from the cleaned up Pharo system and infrastructure.