For Leela Zero it's basically just the computing resources, the software is done using an abstract but openly-specified GPU execution system OpenCL, similar (as

For Leela Zero it's basically just the computing resources, the software is done using an abstract but openly-specified GPU execution system OpenCL, similar (as far as I understand) to an instruction set architecture (ISA). Whether the abstract execution system is implemented in a proprietary or free way is a separate issue. For example these days it's hard to execute x86 instructions without running some sort of proprietary microcode and/or management engine. For comparison, OpenCL has many competing implementations, including the free open source MESA graphics drivers.