Navigation/route finding.

I like abstract strategy games, but I don't like heavy memorization. Chess is popular so it's easy to find opponents, but memorizing the opening book is necessary if you want to get good. It's also very easy for weaker players to lose the game from a single blunder, which is unsatisfying for everybody. Arimaa was designed to be difficult for computers because of the very high branching factor, and that same property also makes it interesting for humans.

Arimaa can be played on a Chess board, and the rules are simple. Memorization is completely useless. You're forced to use intuition, in a way more like Go than Chess. There are no draws. Comebacks from inferior material are much more common than in Chess. It feels like Chess without the boring bits. It's still too new to tell if it's a truly great abstract strategy game, but people are already playing it at a very high level with no obvious flaw in the rules. I recommend trying it:
http://arimaa.com/arimaa/

I've been using a Lamy Safari fountain pen every day for years, dropped it a few times, and it still works good as new. Most fountain pens are fragile and expensive, designed more for asthetics than functionality. The Lamy Safari is reasonably priced and extremely reliable. The grip section has an unusual design that's very comfortable to hold. Even the nibs are tougher than average and if you manage to destroy one (eg. by dropping onto concrete) they are replacable. There's good reason these pens are highly recommended for beginners by fountain pen user groups. It will easily survive long enough to save money over disposable ballpoints if you buy ink in bulk and use a refillable cartridge.

There's a strong argument that the real reason for Japan's surrender was the Soviet invasion of Manchuria, which happened at the same time. You'll note that the Allies did a lot of damage to Japanese cities with conventional weapons without forcing surrender. The firebombing of Tokyo caused similar damage to the bombs. The bombs however were a convenient excuse to avoid losing face, because unlike the Manchuria campaign they couldn't be blamed on Japanese military incompetance.

Hard real time support, and greater electrical robustness. There's no OS or caches changing your timings unexpectedly, and interrupt latencies are very low and consistent. It also sources/sinks a lot more current, so you can do things like driving an LED directly from an IO pin without an external transistor.

Are you using the Arduino library? It's much faster if you access the AVR registers directly.

Slow it down for a bassline and that 192KHz will actually be useful.

Flicker become invisible at about 100Hz, but only when your eyes are perfectly still. As soon as you move your eyes the flicker becomes visible. Saccadic masking does not supress this. I have personally tested this using an LED and a 555 timer, and I can see flicker up to about 10KHz if I move my eyes fast enough. PWM lighting is extremely annoying to me, as well as multiplexed LED displays.

The most legible font is the font you're most familiar with. I used to take fonts very seriously, tweaking Fontconfig settings, etc. I now use default sans-serif for everything. I literally don't know what font it is, and it's just as legible as my customized setup. Despite all the jokes about Comic Sans I doubt it would take more than a week to get used to it.

Stopped breathing doesn't kill instantly. It's not practical with 100s of people, but with only one there should be time to restrain that person and inject them with naloxone.

You can do meaningful mathematics research with nothing but pencil and paper. Filtering out frivolous submissions is a worthwhile goal, but the fee should be adjusted according to the author's ability to pay.