SimCT (Similarity Clustering Tree) is a way to visualize relationships between biological objects (genes, proteins, gene pairs, protein complexes,...) annotated to an OBO ontology. It relies on the notion of similarity between terms of the ontology, which is based on the concept of [precision]of ontology terms.

SimCT does two things:
  clusters objects provided by the user, with respect to the [similarities] of their respective annotations.
  displays the resulting tree(s) using a java viewer.

You can use this tool to define and annotate sub-clusters of similar objects, and tune this level of similarity. You also have the possibility to visualize simultaneously several trees corresponding to different gene groups or ontologies.