If you want to build an alternative Knot implementation (git Hosting) you can use anything as long as the API is compatible ?
Same for all of the parts of Tangled really
Also, even if it's down, unlike GitHub you can self host your own AppView so it's never down for you
Self hosted servers go down too and why people have picked hosted solutions like GitHub, Bitbucket, and GitLab
atproto is a red flag for me now, toxic leaders at bluesky, who effectively control the protocol, it's not really open for others to have a say in what it looks like
you also don't have private repos and you will need to have centralized app view permission addons to have parity with user expectations, given the weak permissioned data proposal bluesky chose (their own proposal that works for what they need)