Electrum

Electrum is a lightweight Bitcoin wallet that lets you send, receive, and hold bitcoin without running a full node. It verifies transactions against the Bitcoin blockchain and keeps your private keys encrypted on your own computer, so funds stay under your control.

It runs on Windows, macOS, Linux, and Android. You can keep keys offline and spend from a watch-only wallet, split spending authority across multiple wallets with multisig, and connect a hardware wallet. Lightning support is included, and a recovery seed phrase restores access.

Electrum is pure Python and is distributed under the MIT license. It connects to decentralized servers, supports third-party plugins, and lets you export your keys with no lock-in.