Tracking & Reporting System Availability

What is being used to track and report on system availability and uptime? Currently, we are using a rather manual process but I would like to know if anyone has a simple, inexpensive product that can automate things a bit. For example we track different types of downtime (enterprise, WAN, isolated, remote users, etc) and different sub-categories (productional or core business hours versus afterhours/weekend). I am sure something could be done in MS Access, but simply don’t have the time.