This server is mainly to test and demo XSS vulnerabilities, specifically postMessage vulnerabilities.
This site is not dangerous, it is for research purposes. There is no backend code, it is a static file server.
https://github.com/jeremy-neale/exploit_server
Basic demo:
https://stat-pad.com/postmessage-demo.html
Bad origin (.includes) check 1 (safe):
https://stat-pad.com/bad_origin_checks/includes.html
Bad origin check 2 (host spoofing, vulnerable):
https://jeremy-neale.github.io.stat-pad.com/bad_origin_checks/includes.html
https://jeremy-neale.github.io/public_vulnerable_exploit_server/