SEMI (Semiconductor Equipment and Materials International)
OASIS (Open Artwork System Interchange Standard) is maintained by SEMI (Semiconductor Equipment and Materials International). The current version is SEMI P39. The register lists it as active. The specification is available to purchase.
SEMI's more compact successor format to GDSII, purpose-built for the enormous file sizes modern multi-patterning and curvilinear-mask layouts produce — the same design information as GDSII, but compressed and structured to stay tractable at advanced nodes.
The full reference entry is for registered members. Registration is free and takes a minute. You come back to this page afterwards.