Short text describing what a bitcoin client is and why it is required to download one as opposed to, say, using a web service...
+Bitcoin is a system of merchants, individuals, a network of participants and software. Together they maintain a mutually co-operating infrastructure without the need for authorities - a decentralised peer-to-peer system. A core layer of the Bitcoin system is the Bitcoin network through which people interact with it using Bitcoin client software. Below we list such software.
+Bitcoin clients are the base level of technology for conducting Bitcoin transactions. Clients usually store a collection of keys on that computer (often termed a wallet). These keys allow you to send and receive payments through the Bitcoin network. Nobody has access to these keys except yourself, and they must be kept secure. This is where clients differ, with ingenious strategies and ongoing research into making a user-friendly and secure client - not an easy task when both goals often conflict!