Logged-in users can import any public app on GitHub into Glitch. To make it easy for them to do so, you can add a link on your GitHub page that will import the repo you specify to Glitch, no account required.
You can also Remix a Glitch app.
Import URL format
Import URLs have the following format: https://glitch.com/edit/#!/import/github/org-name/repo-name
Populate environment variables on import
You can also populate the values in a project's .env file on import. This can be used to automatically set up a project with credentials or config settings already in it. Just pop the variable names and corresponding values on the end of your import URL, like so:
https://glitch.com/edit/#!/import/github/org-name/repo-name?var1=value1&var2=value2...