This paper describes the Enhanced System Monitor (ESM); a multipurpose computer site monitor developed at Pacific MIS for internal use. ESM offers real time monitoring, predictive monitoring, and consulting functions for computer sites. Control Blackboarding techniques were developed to allow model based reasoning to be performed with a simple production rule expert system shell, owing to the lack of more powerful tools in the standard UNIX environment at the time. The project was conducted in a manner unusual for large corporations: Domain personnel were used to build a large scale application and funding was secured in an "entrepreneurial" fashion. The resulting system offers greater flexibility and functionality than comparable commerical monitoring systems and was delivered at a cost of $250,000 -- one eighth the cost of a comparable commercial system. Development, installation and training were completed in only 11 months -- a time frame comparable to deployment of a large commercial system. Based on labor costs during outages, the system is expected to pay for itself in less than 3 years.