Electrum is a free and open-source Bitcoin-only wallet that has been up-and-running since 2011. Electrum is a non-custodial wallet, enabling users to have complete control over their private keys. With strong functionality, high security, and a basic user interface, Electrum may be less beginner-friendly than other popular crypto-currency wallets. Seasoned bitcoiners will appreciate Electrum's advanced features, such as Lightning payment channels and support for hardware wallets.