Which of the following is a medication for anxiety but not classified as a benzodiazepine?

Buspar, or buspirone, is a medication that is used to treat anxiety and is not classified as a benzodiazepine. It operates through a different mechanism compared to benzodiazepines, making it a unique option for anxiety management. It is often preferred in situations where the risks associated with benzodiazepines, such as dependency and sedation, need to be minimized. Buspirone primarily affects serotonin and dopamine receptors, providing an alternative treatment strategy for individuals with generalized anxiety disorder and other anxiety-related conditions.

The other medications listed do not fit the criteria specified in the question. Seroquel, although sometimes used off-label for anxiety, is primarily an antipsychotic and is classified as an atypical antipsychotic. Vistril, also known as hydroxyzine, falls into the category of antihistamines and can be used for anxiety but is not a first-line treatment like buspirone. Xanax is a well-known benzodiazepine used to manage anxiety, thus directly contradicting the requirement of the question.