[chazu]

The Planiverse by A. K. Dewdney is also a great read on this subject - its less of an allegory than Flatland and focuses more on what the physiology and society of 2D life might look like. Worth a look.

[Isamu]

I had this book, it had fun illustrations and thoughts about a hypothetical world.

https://en.wikipedia.org/wiki/The_Planiverse