Most of the Steno tools are written in go.
The source for the Front end tools (Steno, steno-similar) can be found at: https://github.com/bcampbell/steno
The back end tools (scrapeomat, slurpserver etc) are at: https://github.com/bcampbell/scrapeomat
The Steno GUI tool is in quite a bit of flux at the moment.
It originally used the go-qml bindings to provide a Qt/QML GUI. However, go-qml hasn’t really been maintained recently, and packaging up builds with the Qt libraries always got a little awkward.
The current plan is to switch over to a libui-based GUI.
There is a ui branch of steno with a rough proof-of-concept version already working. It’s still missing a bunch of features, but is simple, fast and easy to package. it looks promising.
The Steno tools are released under the Affero GPL (v3).