Electrum Wallet
In short: Electrum Wallet is a Bitcoin wallet with a simple interface that can run on Windows, macOS, and Linux.
Electrum Wallet is a Bitcoin wallet with a simple interface that can run on Windows, macOS, and Linux. It is one of the oldest Bitcoin wallets still in use, and its source code is open for anyone to review.
Why it matters
Electrum is a lightweight wallet: instead of downloading the whole blockchain like a core wallet, it gets the data it needs from Electrum servers, so it is ready to use within moments. Private keys stay on the user's device, backed up by a seed phrase and protected by an optional password that encrypts the wallet file. It also supports hardware wallets, multi-signature wallets, and watch-only wallets that track addresses without being able to spend from them. Because it is popular, fake versions have been used to steal funds, so it is safest to download it only from the official website and verify the download.
Example
A user installs Electrum on a laptop, creates a standard wallet, writes the seed words on paper, and sets a password. When a friend sends bitcoin, the payment appears almost immediately and becomes confirmed as new blocks are added. Later the user connects a hardware wallet to Electrum, so payments are prepared on the laptop while the private keys never leave the hardware device.