One of my most useful tools is invisible, infinitely recyclable, and free — well, in a sense. It’s AIR. You do need another substantial tool (compressor) to use it; but then endlessly refilling your tank only costs the electricity or other fuel to run it. A compressor has so many uses for any serious “maker” that any list is bound to be wildly incomplete. I got my first (largish) machine decades ago to blow water out of copper plumbing pipes that needed soldering.
You only need a hose and cheap end fittings for simple tasks like pressurizing tires and balls, blowing dust out of computer/electronic innards, wood/metal chips out of deeply drilled holes, debris from vehicle vents, clogged vacuum cleaner filters, etc. etc. I’ve also found multiple uses for spray paint gun, abrasive cutoff tool (for metal), air hammer, ratcheting wrench, impact driver (nearly essential if you do any vehicle tire work). My air powered stapler, finish nailer and framing nailer have seen much use in carpentry and fence construction over the years; many other specialized air powered tools exist. When I no longer needed the large compressor, I replaced it with a more compact, less capacious unit that’s incapable of large flow tasks like spraying paint, but still incredibly valuable for almost everything else. Compressors (electric or gas powered) are widely available new and used, from under $100 to well over $1000 — pick a size and quality proportional to the sustained air flow (CFM) you need and how heavily it will be used. — Alex M
6 gal. 1.5 HP 150 PSI Professional Air Compressor from TNM by Central Pneumatic ($160)