Collex is a set of tools designed to aid students and scholars working in networked archives and federated repositories of humanities materials: a sophisticated COLLections and EXhibits mechanism for the semantic web.
Dia is inspired by the commercial Windows program 'Visio', though more geared towards informal diagrams for casual use. It can be used to draw many different kinds of diagrams
Scala is a powerful software tool for experimentation with musical tunings, such as just intonation scales, equal and historical temperaments, microtonal and macrotonal scales, and non-Western scales