bitcoin (P2P electronic cash system)

Bitcoin is a free open source peer-to-peer electronic cash system
that is completely decentralized, without the need for a central
server or trusted parties.  Users hold the crypto keys to their
own money and transact directly with each other, with the help
of a P2P network to check for double-spending.

This Bitcoin client builds the backbone of the bitcoin network.
It downloads, verifies and distributes the blockchain to other
peers in the network. It uses lots of diskspace and bandwidth.
If you just want to send and receive Bitcoins you should look at
a light client like Electrum.

Please make sure to read the release notes first before upgrading:
https://bitcoincore.org/en/releases/0.15.1/

qrencode is an optional but strongly recommended dependency.