Moq (pronounced "Mock-you" or just "Mock") is the only mocking library for .NET developed from scratch to take full advantage of .NET 3.5 (i.e. Linq expression trees) and C# 3.0 features (i.e. lambda expressions) that make it the most productive, type-safe and refactoring-friendly mocking library available. And it supports mocking interfaces as well as classes. Its API is extremely simple and straightforward, and doesn't require any prior knowledge or experience with mocking concepts.
Catch stands for C++ Automated Test Cases in Headers and is a multi-paradigm automated test framework for C++ and Objective-C (and, maybe, C). It is implemented entirely in a set of header files, but is packaged up as a single header for extra convenience.
Midje is a test framework for Clojure. I created it to support top-down as well as bottom-up testing, to encourage readable tests, to provide a smooth migration path from clojure.test and to support a balance between abstraction and concreteness.