We've audited several cryptocurrency related projects having an application that polls bitcoind for new blocks and builds a parallel database of blocks and transactions. This is generally done in order to provide search capabilities, link transactions to user accounts, store auxiliary data for higher level protocols, or to provide block-chain intelligence.
Copay is an easy-to-use multi-signature bitcoin wallet developed by BitPay to significantly decrease the risk of Bitcoin theft. When users join a Copay wallet, more than one person must sign every transaction. Users communicate peer-to-peer and the signing keys are stored locally.