If you are just looking to call a function periodically, use System.Threading.Timer. Using this, it would be easy to write a simple service that performs whatever tasks you want at your chosen intervals.
A good library for scheduling jobs is Quartz.NET. You can either run it as a stand-alone application, or as a part of your own application. It has a very good API with many features out of the box. There is also a tutorial to get you started. It is a port of the Java Quartz scheduling framework.
If you are looking for a replacement to the Windows Scheduler, try VisualCron. It's not free, but it has many features.