Engineering notes from 9io.
How we build products, AI systems and trading infrastructure — and what we learn on the way. Written by the people who do the work, with the sources linked.
iPhone Duo app development: the iOS 27.1 fold APIs in practice
iPhone Duo app development with the iOS 27.1 SDK: how old builds look, the hinge and reserved-region APIs, layouts per posture, Safari and testing.
26 October 2026 · 15 min read GamesFootball Kick: a football game built around iPhone Duo’s fold
Football Kick turns iPhone Duo’s fold into a goal line. How the game, its physics and its keepers work, and how its engine runs free in your browser.
26 October 2026 · 8 min read GamesBitfold: the retro game console app we built for iPhone Duo
Bitfold turns iPhone into a pocket game console with ten original games. How we built it for iPhone Duo, and how to play three of them in a browser.
26 October 2026 · 8 min read GamesThe best retro game apps for iPhone Duo and iPhone in 2026
Retro game apps for iPhone Duo and iPhone as of 26 October 2026: ten apps compared on systems, price, controllers and fold support, and what’s legal to play.
26 October 2026 · 13 min read GamesThe best iPhone Duo games so far, and what each does with the fold
The best iPhone Duo games so far, and what each does closed, folded like a book and in tabletop mode, with prices as of 26 October 2026.
26 October 2026 · 10 min read iPhone DuoThe best apps for iPhone Duo so far, and what each does with the fold
The best apps for iPhone Duo as of 26 October 2026: 23 apps and games by category, what each does closed, open and half folded, and how to check one.
26 October 2026 · 14 min read GamesBest football kick games for iPhone in 2026: penalties and free kicks
The best football kick games for iPhone in October 2026, from penalty and free-kick duels to flick soccer, compared on price, ads, offline play and iPhone Duo.
26 October 2026 · 13 min read