NModbus is a C# implementation of the Modbus protocol. Provides connectivity to Modbus slave compatible devices and applications. Supports serial ASCII, serial RTU, TCP, and UDP protocols. NModbus4 it's a fork of NModbus(https://code.google.com/p/nmodbus). NModbus4 differs from original NModbus in following:

1. removed USB support(FtdAdapter.dll)
2. removed log4net dependency
3. removed Unme.Common.dll dependency
4. assembly renamed to NModbus4.dll
5. target framework changed to .NET 4

To install NModbus4, run the following command in the Package Manager Console

PM> Install-Package NModbus4

Documentation is available in chm format (NModbus.chm)

NModbus4 is licensed under the MIT license.