Mathtoys provides a version of the Prooftoys proof assistant with user interface customized toward solution of high school-level algebra problems. The HTML and code in the mathtoys repository is just the files unique to the Mathtoys web site at http://mathtoys.org/. Almost all of the JavaScript code for Mathtoys is contained in the Prooftoys repository at https://github.com/crisperdue/prooftoys.
The Prooftoys engine itself also has its own web site at http://prooftoys.org/.
See also https://www.pivotaltracker.com/n/projects/248279 for some task information.