Here are some alternatives (some internally use free Wolfram engine):
Reimplementation in Rust: https://github.com/ad-si/Woxi
WLJS Notebook: https://wljs.io
VS Code extension: https://github.com/vanbaalon/wolfbook
> Reimplementation in Rust
It's so disappointing to see CLAUDE.md in projects like these. Basically rules it out for serious use.
There is also SageMath and Mathics. Not replacements but close.