Open Hypermedia have come up with several systems, which can provide services to software developers. This paper argues that usability is a critical attribute that should be taken into consideration during the development process of an Open Hypermedia System (OHS). An analysis of the usability issue from a developer’s perspective is carried out. Moreover, targeting at a usability estimation technique, a questionnaire for OHSs designers is being proposed. Finally, some evaluation results of numerous existing systems are being presented and discussed. Keywords usability, hypermedia, hypermedia development