What are some projects that have taken advantage of Bitcoin's taproot upgrade so far?

Projects that support paying or receiving to P2TR addresses are tracked here.

A non-exhaustive list of projects that are working on doing more interesting things taking advantage of Taproot block space savings and improved privacy: Bitcoin Core, rust-bitcoin, btcd, secp256k1-zkp (MuSig2 and FROST), lnd/Taro, Taproot wallets (e.g. TapWallet), Taproot scripting tooling (e.g. btcdeb, Script Wizard). There has been a lot of discussion on the lightning-dev mailing list and elsewhere on how the Lightning Network protocol could upgrade to take advantage of Taproot but at the time of writing that is still at the discussion phase.

Some additional Taproot use cases are listed here.

I'm still trying to understand what can be built with this taproot feature.

For the most part Taproot doesn't support any new functionality (there were no new opcodes added with completely new functionality, just a replacement for OP_CHECKMULTISIG and a tweak to undefined opcodes), what you could do before Taproot you can do after Taproot just with block space savings and improved privacy.

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