Simple Bitcoin Wallet (aka SBW) is an open-source, reproducible, non-custodial, autonomous wallet for Android. Besides basic wallet functions it has a number of advanced features such as Multiwallets, RBF, CPFP and more.
v2.5.4: "The single most important innovation here is that now you can send transactions from multiple attached wallets at once, to save on fees and easily consolidate your UTXOs."
"For example, in a video below sender has two wallets: a default one which comes with an app and a second one which was attached later (by providing another mnemonic)."
"Sender then utilizes both of these wallets to send a single transaction into receiver wallet (receiver by the way only has a hardware wallet and no signing wallets at all, that's another new feature)."
"Sender then realizes his mistake and cancels a transaction using RBF, both wallets react to this appropriately."
v2.5.5: "Now you can use built-in search to look for addresses belonging to your wallet and then use a found address to sign any message."
"Signing and verification is implemented according to BIP322 and is compatible with other wallets who also implement it (I've reused low level BIP322 code from Sparrow wallet, thanks to them for saving me some time)."
"On top of BIP322 I've come up with a "BIP322Share" format to make all signing and verification parts portable and easy to use on mobile devices."
"Link to BIP322Share description can be found here. Other wallets are welcome to implement it to make signing and verification more accessible.