The on-line monitoring interface specification OMIS provides means for developing more powerful tool environments for parallel and distributed systems. It specifies the interaction between any tool and a monitoring system which is responsible for observing and manipulating the programs' execution. By having this well defined interface it is now possible to concurrently use several tools of possibly different developers with the same program run. The research group at LRR-TUM currently designs an OMIS compliant monitoring system for PVM running on workstation clusters. Tool developers can use this implementation to attach their own on-line tools to the system.