Infocom Frotz builds Frotz with Emscripten so that Infocom's multimedia games can be played online.
The game files were obtained from The Obsessively Complete Infocom Catalog, the media files from the IF Archive, and the manuals from the Infocom Documentation Project. They are proprietary documents whose copyright belongs to Activision.
Infocom's non-multimedia games should be played with Parchment instead.
See the Infocom Frotz Github page for the interpreter's source code. Infocom Frotz is GPL-2.0 licensed.