The SqlMonitoring tool makes it possible to monitor SQL 2000, 2005, 2008 environments and send alerts to a central database (SQL 2008). A client can be used to view the alerts en perform actions on them. This tool is a good alternative if you do not have the budget or infrastructure for tools like SCOM. Sql Monitoring FAQ
This tool was designed to be an open source alternative for tools like SCOM 2007 and BMC Patrol. The tool also focusses primarly on SQL Server.
The feature complete version will be released on August 30th but this version is complete for as far as the service is concerned. Most work has to be done on the client, but the basics are available.
For a quickstart download the binaries and follow the steps in the included Quick Start Guide. To run the tool you will need at least SQL Server 2008. Any version will work, although for large environments it's recommended to use the Standard or Enterprise edition.