When I worked at Google, we made a prototype of a non-grid spreadsheet-type thing. More graphical than tree-like, but the same underlying engine could be used for other purposes.

Videos:

1. The FLOW Shell: https://drive.google.com/file/d/0B6Qg3A0fSZHoNk5EX3ZkREEwbUk...

2. FLOW 2D Turtle Graphics: https://www.youtube.com/watch?v=4wO_RrftJTE

3. Background: https://www.youtube.com/watch?v=-fbq-_H6Lf4