This article is a stub. One of us will have to go and actually verify with the executable.
FreeZZT is a fork of ZZT developed by zzo38 in 2020. It is available under the terms of the MIT license.
FreeZZT includes some enhancements and bug fixes for working with standard ZZT files (format number -1), but also supports an extended format (format number -4) with some new features.
The source repository also includes an external editor, which is compatible with both world formats. This is currently the only known program other than FreeZZT itself which implements this format.