galaxa-web.js and its worklets bundle jsbeeb (https://github.com/mattgodbolt/jsbeeb),
commit f2781a308c651bba1966569644e803b571a5aeda, licensed under the GPL version 3 or later: see LICENSE-jsbeeb.txt.
The rest of the bundle's source is tools/web/play.js in this repository.
The BBC ROMs are not included: the page loads them from https://bbc.xania.org/.