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So it seems like OKAD is basically a layout editor, simulator, DRC checker, and GDSII compiler. The simulator uses a very simplistic transistor model that would only work at very old process nodes (>350nm?) due to the low impact of parsitics and leakage.
Not even a moderately complex digital chip from the mid-90s could be designed and verified using such a simplistic toolchain.
To provide a software analogy, Chuck wrote an assembler for a custom assembly dialect targeting e.g. x86, and then directly used that assembler to build an operating system kernel. Given the absence of "higher-level" constructs, the resulting OS will never be as complex as something like an NT kernel, especially due to the difficulty of testing and verification.
Going back to circuit design, OKAD will never be able to design a complex digital chip on a state-of-the-art process. It's really nothing more than a simplistic EDA toolchain that would only work on simplistic circuits and fabrication processes.
A modern EDA toolchain from e.g. Cadence is many orders of magnitude more complex.