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sudo apt-get install squeak squeak-vm squeak-sources3.9 squeak-image3.9
After that, Squeak is available from the Programming submenu. Shown above is the end Squeak workspace.
What to do after this I'm not quite sure. Looks fun, though.
Managing day-to-day stuff with Ubuntu
sudo apt-get install squeak squeak-vm squeak-sources3.9 squeak-image3.9