"Electrum is an easy to use Bitcoin wallet. It protects you from losing coins in a backup mistake or computer failure, because your wallet can be recovered from a secret phrase that you can write on paper or learn by heart. There is no waiting time when you start the client, because it does not download the Bitcoin blockchain.
Instant on: Your client does not download the blockchain. It uses a network of specialized servers that index the blockchain.
Forgiving: Your wallet can be recovered from a secret seed.
Safe: Your seed and private keys are encrypted on your hard drive. They are never sent to the servers.
Low trust: Information received from the servers is verified using SPV. Servers are authenticated using SSL
No downtimes: Your client is not tied to a particular server; it will switch instantly if your server is down.
Ubiquitous: You can use the same wallet on different computers, they will synchronize automatically.
Cold Storage: Sign transactions from a computer that is always offline. Broadcast them using a machine that does not have your keys.
Reachable: You can export your private keys into other Bitcoin clients.
Established: Electrum is open source and was first released in November 2011."