The branch called "canary" is a public beta version of the game, complete with new experimental features and probably bugs, too. It's an incrementally updated version of the update that's going to be pushed out at the end of October.
Here's how to access it:
- Right click the name of the game in your Library. Hit "Properties".
- A window titled "Little Square Things - Properties" should pop up. Click the BETAS tab.
- Underneath "Select the beta you would like to opt into:", you'll probably see "NONE". Click that and select "canary". Leave the "beta access code" blank.
- You should then see "Successfully opted into the 'canary' content beta." Then, after the new branch downloads, your Library list should change to "Little Square Things [canary]".
You can revert to the main version by following those steps and selecting "NONE" again.
Canary has Undo fully implemented, with more stuff to come soon.
Happy Squaring!