DotNetMQ is an open source Message Broker that has several features:

• Persistent or non-persistent messaging.
• Guaranteed delivery of persistent messages even in a system crash.
• Automatic and manual routing of messages in a custom machine graph.
• Supports multiple databases (MS SQL Server, MySQL, SQLite, and memory-based storage for now).
• Supports don't store, direct send style messaging.
• Supports Request/Reply style messaging.
• Easy to use client library to communicate with the DotNetMQ Message Broker.
• Built-in framework to easily construct RMI services upon message queues.
• Supports delivering messages to ASP.NET Web Services.
• GUI-based management and monitoring tool.
• Easy to install, manage, and use.
• Written entirely in C#.

See detailed documentation: http://www.codeproject.com/Articles/193611/DotNetMQ-A-Complete-Message-Queue-System-for-NET