@genofire see https://hacktoberfest.digitalocean.com/ for details on Hacktoberfest. I don't know of a GitLab-specific t-shirt, but while the last years you could only participate via Github, this year you can via GitLab too. You can even register with your GitLab account. And our (F-Droid's) repos are properly labeled for Hacktoberfest participation. So just start your MRs at fdroidclient, fdroiddata, fdroidserver or any of the others (having the label or not 😄).
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