Puts something running on your machine on the internet, under a subdomain you picked, without a quota or a monthly bill for the privilege. Run the server yourself, or point it at ngrok or Cloudflare Tunnel if you would rather not.

HTTP and TCP, and TCP streams byte by byte, which is the difference between a demo that plays a video and one that waits for it. Self-hosting is one command and a wildcard DNS record: certificates and access tokens are handled from there, and named tunnels live in a config file so the second time costs nothing.