CirQit2.1 is a non-CNF QBF solver that uses a circuit representation. It is based on a prototype originally developed by Vicky Iverson, it has since been rewritten and expanded by Alexandra Goultiaeva under the supervision of Fahiem Bacchus.
Its most notable new feature is dual propagation, which allows solving both the problem and its negation at the same time.
CirQit2.1 has solved the most problems in the non-prenex non-CNF track of QBFEval'10.