OPRTN is a Bitcoin-only, self-custodial Android wallet.

Your keys are generated and stored on your device. There is no account,
no signup, no custodian, and no telemetry.

Write a message onto Bitcoin. Any transfer can carry a short message,
written into an OP_RETURN output. Once the transaction is mined that
message is part of the blockchain — it cannot be edited and it cannot be
deleted. OPRTN also reads messages back off any transaction that carries
one, including transactions sent by other people.

Wallets: legacy, SegWit and Taproot, plus multisig and watch-only.
Connect to your own Electrum server or Bitcoin node.
Coin control and fee bumping.
Encrypted storage with plausible deniability.

On-chain only. There is no Lightning in this wallet.