Just in time for the start of Hilchos Kiddush Hachodesh in the Rambam’s daily learning cycle, a groundbreaking new app makes one of the most technically demanding sections of Mishneh Torah actually enjoyable to learn.

The app is clean, well-designed, and genuinely fun to use. Each of its 38 lessons – covering all 19 chapters of Hilchos Kiddush Hachodesh – is built around vivid visuals, real-time simulations, and hands-on interactive tools that turn dense halachic and astronomical content into something you can see, play with, and actually understand.

The scope is impressive and takes users through the full arc of the Rambam’s system: the halachos of witnesses and the ancient calendar beis din, the mathematical structure of the fixed calendar, and the sophisticated astronomical calculations the Rambam uses to determine whether the new moon is visible at the start of each month.

But it’s the interactivity that makes it stand out.

Want to understand how the Rambam’s visibility rules work? A live color-coded display lets you input the moon’s position and see instantly whether it’s visible or not.

Trying to wrap your head around the 19-year leap year cycle? An animated simulator runs through all 19 years and shows the exact moment the lunar and solar calendars sync back up.

There’s even a cross-examination module that puts you in the seat of a Sanhedrin judge, testing witness testimony against pre-calculated data – making clear why the Rambam dedicated so many chapters to astronomy in the first place.

The app includes dozens of additional tools, diagrams, calculators, and interactive displays – covering everything from how the Molad is calculated, to why certain days can never be Rosh Hashana, to how the moon looks different depending on where in the world you’re standing, and much more.

The original Rambam text accompanies every lesson, with Hebrew and English side by side, and an option to test yourself is available at the end of every lesson.

The app is available here.