OASIS
Beginner
A newer, more compact file format for chip drawings.
Novice
Open Artwork System Interchange Standard (SEMI P39, version 1.0 in 2004), a successor to GDSII that stores the same cells and shapes in much smaller files.
Expert
Compacts with variable-length integers, short records for rectangles, modal variables that let a record omit values repeated from the previous one, repetition records for arrays and irregular sets of identical shapes, and optional compressed cells. Fill and post-OPC data benefit most.