I haven't used Squash before so thank you for teaching me something new.

Both appear to be relatively similar in terms of features. Squash has a different approach as to how items are organized and probably the workflows around this organization.

Squash appears to be a Windows exe, although written in Java. Kiwi TCMS is distributed as a Docker image and is fully supported on Linux. Kiwi TCMS is written with Python and Django.

Both are open source and have online demos. For Kiwi TCMS you can register for a full-featured demo. For Squash it looks like you can use one of their pre-selected accounts.

Squash appears to have more fancier charts though.

Disclaimer: I am the project lead for Kiwi TCMS.