Retractor is a Javascript application for exploring retrograde analysis chess problems (often called retro problems) in your browser. In a retro problem, you play chess backwards to deduce information about the history of a game, such as what the last 5 moves were or on what square the black queen was captured. A tutorial on retro problems is available in the application (see the "About" section on the github page for a link to the currently hosted location).
If you would like to run the code locally, you should check out the repository and start a web browser in the repository
directory. If you have Python 3 installed, you can use python -m http.server 8000 to start a web server
(for Python 2, use python -m SimpleHTTPServer 8000). Then open http://localhost:8000/retractor.html in your browser.
Opening the retractor.html file directly from your browser probably won't work, because of CORS
restrictions for local files on the latest browsers. If you really cannot get anything else to work, you can look up how
to disable such restrictions in your browser, but this is not recommended.
If you want to run the tests, you should install Jasmine. You want the standalone version
that can be run in a browser. Place the Jasmine installation in a directory called jasmine in the root directory of
the repository. Then http://localhost:8000/tests/test.html will run the tests. The latest version of Jasmine that has
been verified to run the tests is 4.5.0.