Looks like it’s a web-based hot wallet first released in 2015. Predates modern best practices around key material security.

GitHub

Releases · OutCast3k/coinbin

Javascript Bitcoin Wallet. Supports Multisig, Stealth, HD, SegWit, Bech32, Time Locked Addresses, RBF and more! - OutCast3k/coinbin

Interesting, I think it's still used to publicly share verification data by some.

I haven’t looked at the capabilities, but it would be reasonable to use for, say, getting an address from a recipient’s XPUB. Something like that. If you wanted to use it offline with TailsOS, that could make sense, if it was just one part of a multisig quorum. I would NOT recommend using it as a single-sig wallet, especially not online. Risk of leakage too great.

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