Quartz.NET is a full-featured, open-source job scheduling system that can be used from smallest apps to large-scale enterprise systems. Can run embedded within an application or even instantiated as a cluster of stand-alone programs (with load-balance and fail-over capabilities). Jobs are scheduled to run when a given trigger occurs, triggers support wide variety of scheduling options.
DotNetMQ is a message broker (message queue, message oriented middleware) that has several features including guaranteed delivering, routing, load balancing, server graphs... so on. See article on CodeProject.com for more information: http://www.code