Runebender is a free and open-source font editor built on the Linebender ecosystem of Rust crates.
There are currently two maintained front-ends, Xilem and GPUI. The default front-end for now uses GPUI and runs both cross-platform natively on desktop and in the browser. The Xilem version is more experimental and less usable, but could be interesting as an example of a Xilem application.
Quick Install
Install the editor with cargo.
cargo install --git https://github.com/eliheuer/runebender-gpui Then open a font from anywhere.
runebender-gpui path/to/Font.designspace