This paper presents a multi-user collaborative infrastructure, SCAPE (an acronym for Stereoscopic Collaboration in Augmented and Projective Environments), which is based on recent advancement in head-mounted projective display (HMPD) technology. The SCAPE mainly consists of a 3'x5' interactive workbench and a 12'x12'x9' room-sized walk-through display environment, multiple head-tracked HMPDs, multi-modality interface devices, and a generic application-programming interface (API) designed to coordinate the components. The infrastructure provides a shared space in which multiple users can simultaneously interact with a 3D synthetic environment from their individual viewpoints. We detail the SCAPE implementation and include an application example that demonstrates major interface and cooperation features.