Love it or hate it, the plank is one of the best exercises for strengthening your core. But actually planking -- maintaining what amounts to a stiff, unmoving push-up, where you strive to keep your whole body rigid, like a plank of wood -- can be a little boring. That's where the the Stealth Core Trainer comes in.
It looks like a fancy padded board on top, with a sphere on its underside that sits in a base module. The design allows you to swivel from side to side and up and down as you hold the plank position, ideally with your body perfectly parallel to the ground. You then plop your smartphone down on the board and launch one of the planking games in the companion app -- two are always free and there's a monthly subscription for additional "premium" games.
The basic model, which should work for most people, is now on sale for $99 (it lists for $149). With shipping times delayed due to the pandemic, it takes a couple of weeks to arrive but you can tell mom it's in the mail.