Initially released as XCoin, then known as DarkCoin, Dash is a cryptocurrency aimed at bringing privacy back to transactions. This is something the Dash community feels Bitcoin has lost. Dash changed its name so as to distance itself from the growing notoriety of the DarkWeb. Dash uses X11, which is a chained hashing algorithm, instead of SHA-256 like Bitcoin, or Scrypt like Litecoin. This method allows CPUs and GPUs to both compete in mining.
Dash uses Darksend as a method of achieving privacy in transactions. For this, it uses Masternodes. These are similar to Bitcoin tumblers, in a way. Transactions are all sent to a Masternode. Identical inputs are all into one transaction with various outgoing transactions. This process can be done multiple times to increase the obfuscation of the transactions. You can find out more about Dash at www.dashpay.io