user136944: The question of GitHub alternatives has been raised and closed. Alternative, backup repos exist.
That said, I have not seen any contingencies for planning the social move to those repos and organizing developer efforts for maintaining Core in the face of a GitHub ban.
It seems inevitable, given the recent experiments with banning individual developers or entire projects.
Existing guidelines for contributing to Core seem to exclusively revolve around GitHub.

Contributing to Bitcoin Core
A Gentle Introduction to Bitcoin Core Development
Bitcoin Core PR Review Club

In the event of GitHub banning Core maintainers or Core itself, where do developers gather to communicate and collaborate for reliable development and maintenance of Bitcoin?

user47827: To date GitHub has restricted developer accounts from Iran, Crimea, Cuba, North Korea and has taken down certain projects (e.g. an Ethereum open source privacy project Tornado Cash though Tornado Cash is now back up). GitHub is owned by a US corporation (Microsoft) and is clearly at a minimum bound by US law and US sanctions. There seems to be evidence that it is willing to take actions beyond what it is required by US law and US sanctions though as you suggest.

I have not seen any contingencies for planning the social move to those repos and organizing developer efforts for maintaining Core in the face of a GitHub ban.

No such plans have been made public as far as I'm aware. Recall that no maintainer or no contributor can bind the project to a particular future contingency plan even if they drafted such a plan.

It seems inevitable, given the recent experiments with banning individual developers or entire projects.

It is certainly a possibility but I would say "inevitable" is a bit strong. The best case scenario is GitHub realized that taking down Tornado Cash was an error, reversed that decision and won't pursue similar actions in future for other privacy projects, let alone full node implementations. The worst case scenario is GitHub takes down Bitcoin Core, all other Bitcoin open source projects and restricts the accounts of maintainers and contributors to these projects. Clearly if the worst case scenario happens a plan will have to drafted and executed but I suspect most maintainers and contributors have their fingers crossed that it won't get much worse than the best case scenario. I don't know of any long term contributors that have been impacted by the Iran, Crimea, Cuba, North Korea etc restrictions.
So thus far the GitHub actions haven't caused enough pain on the project to motivate a serious effort to plan for a move away from GitHub. I'm not saying that this is right or wrong, merely that that's the reality. It would be a headache to execute (choosing the replacement, updating docs, potentially worsening the new contributor experience) and many contributors like the convenience, user interface and funding initiatives on GitHub. If the pain increases and we start to move closer to the worst case scenario and away from the best case scenario I am sure we will see more activity and interest in this area.

In the event of GitHub banning Core maintainers or Core itself, where do developers gather to communicate and collaborate for reliable development and maintenance of Bitcoin?

It would most likely be discussed on Libera IRC (#bitcoin-core-dev channel), the Bitcoin dev mailing list and Bitcoin Core dev mailing list. Bitcoin Optech and bitcoincore.org would also be possible sources of information.
Disclaimer: This is just my personal view, no one can speak for the Bitcoin Core project (and certainly not me) but I hope this is somewhat helpful.
This topic was also discussed at the recent Core dev meeting (Bryan Bishop transcript).

136944: <p>The question of GitHub alternatives has been raised and <a href="https://bitcoin.stackexchange.com/questions/99634/what-are-some-of-the-github-alternatives-that-you-consider-for-bitcoin-core-and">closed</a>. Alternative, backup repos exist.</p>
<p>That said, I have not seen any contingencies for planning the social move to those repos and organizing developer efforts for maintaining Core in the face of a GitHub ban.</p>
<p>It seems inevitable, given the recent experiments with banning <a href="https://twitter.com/TheBlueMatt/status/1578533682800865280" rel="nofollow noreferrer">individual developers</a> or <a href="https://cryptobriefing.com/tornado-cashs-code-is-back-on-github/" rel="nofollow noreferrer">entire projects</a>.</p>
<p>Existing guidelines for contributing to Core seem to exclusively revolve around GitHub.</p>
<ul>
<li><a href="https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md" rel="nofollow noreferrer">Contributing to Bitcoin Core</a></li>
<li><a href="https://bitcointechtalk.com/a-gentle-introduction-to-bitcoin-core-development-fdc95eaee6b8" rel="nofollow noreferrer">A Gentle Introduction to Bitcoin Core Development</a></li>
<li><a href="https://bitcoincore.reviews/" rel="nofollow noreferrer">Bitcoin Core PR Review Club</a></li>
</ul>
<p>In the event of GitHub banning Core maintainers or Core itself, where do developers gather to communicate and collaborate for reliable development and maintenance of Bitcoin?</p>
 47827: <p>To date GitHub has <a href="https://github.com/1995parham/github-do-not-ban-us" rel="nofollow noreferrer">restricted</a> developer accounts from Iran, Crimea, Cuba, North Korea and has taken down certain projects (e.g. an Ethereum open source privacy project <a href="https://github.com/tornadocash" rel="nofollow noreferrer">Tornado Cash</a> though Tornado Cash is now back up). GitHub is owned by a US corporation (Microsoft) and is clearly at a minimum bound by US law and US sanctions. There seems to be evidence that it is willing to take actions beyond what it is required by US law and US sanctions though as you suggest.</p>
<blockquote>
<p>I have not seen any contingencies for planning the social move to those repos and organizing developer efforts for maintaining Core in the face of a GitHub ban.</p>
</blockquote>
<p>No such plans have been made public as far as I'm aware. Recall that no maintainer or no contributor can bind the project to a particular future contingency plan even if they drafted such a plan.</p>
<blockquote>
<p>It seems inevitable, given the recent experiments with banning individual developers or entire projects.</p>
</blockquote>
<p>It is certainly a possibility but I would say &quot;inevitable&quot; is a bit strong. The best case scenario is GitHub realized that taking down Tornado Cash was an error, reversed that decision and won't pursue similar actions in future for other privacy projects, let alone full node implementations. The worst case scenario is GitHub takes down Bitcoin Core, all other Bitcoin open source projects and restricts the accounts of maintainers and contributors to these projects. Clearly if the worst case scenario happens a plan will have to drafted and executed but I suspect most maintainers and contributors have their fingers crossed that it won't get much worse than the best case scenario. I don't know of any long term contributors that have been impacted by the Iran, Crimea, Cuba, North Korea etc restrictions.</p>
<p>So thus far the GitHub actions haven't caused enough pain on the project to motivate a serious effort to plan for a move away from GitHub. I'm not saying that this is right or wrong, merely that that's the reality. It would be a headache to execute (choosing the replacement, updating docs, potentially worsening the new contributor experience) and many contributors like the convenience, user interface and funding initiatives on GitHub. If the pain increases and we start to move closer to the worst case scenario and away from the best case scenario I am sure we will see more activity and interest in this area.</p>
<blockquote>
<p>In the event of GitHub banning Core maintainers or Core itself, where do developers gather to communicate and collaborate for reliable development and maintenance of Bitcoin?</p>
</blockquote>
<p>It would most likely be discussed on Libera IRC (#bitcoin-core-dev channel), the <a href="https://lists.linuxfoundation.org/pipermail/bitcoin-dev/" rel="nofollow noreferrer">Bitcoin dev mailing list</a> and <a href="https://lists.linuxfoundation.org/pipermail/bitcoin-core-dev/" rel="nofollow noreferrer">Bitcoin Core dev mailing list</a>. <a href="https://bitcoinops.org/" rel="nofollow noreferrer">Bitcoin Optech</a> and <a href="https://bitcoincore.org/" rel="nofollow noreferrer">bitcoincore.org</a> would also be possible sources of information.</p>
<p>Disclaimer: This is just my personal view, no one can speak for the Bitcoin Core project (and certainly not me) but I hope this is somewhat helpful.</p>
<p>This topic was also discussed at the recent Core dev meeting (Bryan Bishop <a href="https://btctranscripts.com/bitcoin-core-dev-tech/2022-10-11-github/" rel="nofollow noreferrer">transcript</a>).</p>
