AutoDiff.NET is a pure .NET library that allows a developer to easily compose functions symbolically and then automatically calculates the function's value and gradient at any given point. It can be very useful in conjunction with a gradients-based optimization library. It has been tested to work on Mono 2.10 on Linux and on .NET4 on Windows.
Hybrid HTTP API Tester is a general purpose API tester GUI. You can specify a URL and send GET or POST requests to it as a client with an interface allowing you to set up a database of API commands and their parameters. It is useful for probing 3rd party APIs or building your own.