user38458: Bitcoin main net was launched on January 3, 2009 at 19:15:05 UTC. But what is the history of the two other network options in Bitcoin: testnet and regtest?
I think testnet is on version 3, what was version 2, 1 (and 0)? And when was the regtest option added to Bitcoin Core?

user-1: Regtest was added in version 0.9.0 which was released in March 2014

Add '-regtest' mode, similar to testnet but private with instant block generation with 'setgenerate' RPC.

https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.9.0.md
Testnet's history: Has the TestNet ever been reset?
There is one more chain which is used for testing: Signet
It was added in https://github.com/bitcoin/bitcoin/pull/18267 (2020)

38458: <p>Bitcoin main net was launched on January 3, 2009 at 19:15:05 UTC. But what is the history of the two other network options in Bitcoin: <code>testnet</code> and <code>regtest</code>?</p>
<p>I think <code>testnet</code> is on version 3, what was version 2, 1 (and 0)? And when was the <code>regtest</code> option added to Bitcoin Core?</p>
 -1: <p>Regtest was added in version 0.9.0 which was released in March 2014</p>
<blockquote>
<p>Add '-regtest' mode, similar to testnet but private with instant block generation with 'setgenerate' RPC.</p>
</blockquote>
<p><a href="https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.9.0.md" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.9.0.md</a></p>
<p>Testnet's history: <a href="https://bitcoin.stackexchange.com/questions/9975/has-the-testnet-ever-been-reset">Has the TestNet ever been reset?</a></p>
<p>There is one more chain which is used for testing: Signet</p>
<p>It was added in <a href="https://github.com/bitcoin/bitcoin/pull/18267" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/pull/18267</a> (2020)</p>
