every game starts out as the handmade creation of the inventor, which eventually becomes a standardized and mass produced product; but sometimes the commercial versions of games are not available, too expensive, or just not nice enough
Nice little guide to building an IR transceiver - uses the USB port for stable 5V, but includes a link in the comments to a decent circuit diagram that uses a voltage regulator and therefore doesn't need the USB port for power.
Weekend Project Podcast: Make simple radios to listen too. These were made with materials that they could get their hands on and were small enough to carry around in a big pocket.
If your own water is safe from heavy metals, but you still like the way water tastes when it's been through something like a Britta filter, there's an easy way to convert the filter to be reusable, saving a ton of waste and a bit of money.