Rolling your own, for better or worse.
Internet: Running your own AS.
Hair electrolysis machine: happy for the author, I’m still terrified.
Ferrofluid: involving “the wonderfully smelling and somewhat neurotoxic hexane.”
Lasers…, well, think carefully.
I am not safety-concious enough to safely build a laser projector. Even if there are really cool things you can do with one (note the safety gear there!) Not after reading some of Phil Broughton’s scary stories.
HTML “parser”: bots sometimes look for links without parsing the HTML.
File access library: it’s actually quite hard to open a file, and that’s the kind of bug Rust won’t catch.
And: don’t roll your own core web UI elements.