Remembering Cliff Sekel (InsaneDarwin)

January 3, 2026 - PD-Team

The PureDarwin project has lost its leader.

Cliff Sekel, known throughout the community as InsaneDarwin, passed away in November 2025. For many years, and unequivocally in its most recent era, Cliff was the leader of the PureDarwin project and the steward of its community. He was the person who kept the project alive when it would have been easy (and understandable) to let it quietly disappear.

PureDarwin exists today because Cliff refused to let it die.

Leadership Through Action

Cliff did not lead by title alone. He led by doing the hardest work in the project: untangling incomplete source releases, understanding undocumented system behavior, and pushing forward despite the reality that modern Darwin is no longer fully open.

Under Cliff’s leadership, PureDarwin produced its first real, bootable build in many years — PureDarwin 17.4 — marking a turning point from archival effort to living system. That build was not the result of a single patch or workaround, but of sustained, system-level understanding and careful integration across kernel and build tooling. It was by no means ready to use by end-users, but proof to the FOSS community that the last open-source remnants of Darwin could still be turned into a functional operating system.

Direct Engagement with Apple

Cliff was not advocating from the sidelines. For years until his passing he engaged directly with Apple engineers and developers to try and get Apple to open-source important components to make Darwin viable again.

His advocacy around missing components, particularly in networking and system libraries, came from firsthand knowledge, not speculation. While not all of those components were ultimately open-sourced, his efforts helped define the boundaries PureDarwin had to navigate and influenced how the project approached re-implementation and long-term viability.

A Champion of Free and Open Systems

At his core, Cliff was a Free and Open Source Software advocate. He believed deeply that systems should be understandable, inspectable, and buildable by the people who run them. PureDarwin was a challenge to him, although not in the sense of an academic exercise or nostalgia project. It was the belief that Darwin deserved to exist outside of proprietary walls.

He was drawn to hard problems. The harder the system, the more motivated he became to understand it fully. Missing sources, opaque binaries, and shifting interfaces were challenges to be solved, not excuses to stop.

A Community Held Together by One Person

Beyond code, Cliff held the PureDarwin community together. He answered questions, mentored contributors, curated repositories, and kept institutional knowledge alive. For many, he was the first point of contact and the final authority — not because he demanded it, but because he earned trust through competence and consistency.

PureDarwin was not just something he worked on. It was something he carried.

Continuing His Work

Cliff Sekel leaves behind more than repositories and build scripts. He leaves behind a revived project, a working system, and a community that once again believes PureDarwin is possible.

Honoring his legacy means continuing the work with the same care, patience, and insistence on understanding that defined his leadership.

Thank you, Cliff. For the project you rebuilt, for the community you led, and for showing us that even the hardest problems are worth facing.

— The PureDarwin Project