TackMath

Tack Math is an upwind sailing computer. Lay it flat on the deck of your sailboat, pointing toward the bow, and set the angle to your boat's highest angle of attack upwind (as close hauled as you can get). The app will sense your tack based on the heel of the boat, and plot your heading post-tack. As you come about, you can watch the binnacle (or working compass on the app), and align to the green bearing shown before you tack. (It also lets you take a bearing before you tack of your new heading, by following the green dashed line of sight on the screen. The app also returns heel angle and speed in knots. Offers night mode in red as well.