Hey Product Hunt,

Most interview prep teaches you to recognize patterns. Senior interviews get hard one question later: why did you make that choice, what happens when it fails, and what did you trade away?

I got through interview loops without really understanding systems deeply. I could draw the boxes, but I couldn't always defend them. So I built the thing I wished I'd had.

CalibreOS is built around that follow-up question:

Learn. Guides that go past the first answer: real numbers, the production tools, and the design each choice rejected and why.
Practice. Code that runs in your browser, and a system design canvas where a rubric scores you live as you build, with interviewer follow-ups along the way.
Calibrate. Quizzes ask how sure you are before you answer, then show whether "certain" actually meant right. Confident misses come back at 1, 3 and 7 days.
Paths. Pick your role and your interview date, and the plan tells you honestly whether the hours fit.
Digest. Every Sunday, one real incident with a weak answer next to a strong one.

It covers system design, low level design, DSA, ML system design, GenAI and agents, and AI product management.

Free to start. Pro is a one-time payment with no subscription, because interview prep has an end date.

Product Hunt offer: use code PHOFF15 for 15% off any Pro plan, valid for the next 3 days.

I'd love blunt feedback, and one question for you: which follow-up has caught you out in a real interview? I'll reply to every comment.