Microsoft's Infer.NET is essentially an automated system for variational (/expectation-propagation) inference. It implements primitives for common operations an

Microsoft's Infer.NET is essentially an automated system for variational (/expectation-propagation) inference. It implements primitives for common operations and distributions, and then uses the local structure of mean-field inference ("variational message passing": http://www.jmlr.org/papers/volume6/winn05a/winn05a.pdf http://www.jmlr.org/papers/volume6/winn05a/winn05a.pdf) to build up variational inference algorithms for arbitrary factor graphs. It's not infinitely flexible and doesn't solve all problems related to variational inference, but once you get used to it you can iterate quite quickly on model refinements, inference tweaks, etc. without any tedious derivations.