OSLib is a highly optimized interface library for the Application Programmers' Interface (API) for the Acorn series of 32 bit RISC OS computers. It is a useful tool for application program writers for this platform. It is of no use for any other platform.

OSLib provides a complete coverage of the RISC OS API (the so-called SWIs) as a set of C/C++, ARM assembler and Vala headers, together with a thin veneer library.