This paper describes a set of tools which allow the large number of ontologies available on the SemanticWeb to be discovered and reused for other applications (both in the Semantic Web and by the larger knowledge engineering community). Firstly, these tools address the problem of finding an existing ontology, with given characteristics. Secondly, we discuss tools which allow the knowledge engineer to detect and repair errors which occur in the ontology's vocabulary (CleOn) or are related to logical coherency/inconsistency (RepairTab). Once a knowledge engineer is satisfied that the ontology is lexically and semantically consistent, then he/she can extend the ontology if the application requires that. Once the extension has been done, it again would be prudent to use those same tools to check that the resulting ontology is consistent.