Netduino uses .Net Micro Framework and our C# library currently supports .Net Micro Framework 4.2, 4.3 and 4.4. This library provides a nicer MQTT interface fine-tuned and extended with specific features provided by emitter.io. The library is based upon the M2MQTT library written by Paolo Patierno and released under Eclipse Public License.
More information can be found on the .NET / C# download page.