I've tried, but never came to understand Open Transactions, but I understood this without even reading. If they are similar, OT made a really poor job explaining itself.
Open Transactions is definitely a similar project and has some really sophisticated financial features. However, our aim is a little different; we want to focus on one thing -- ledgers -- and ensure that it's as simple and easy-to-use as possible, but with a high level of trust because the service is replicated by a number of different parties.