Cool stuff people made today - what's your favorite?

Scrolling through the feed and saw some really interesting stuff people have been working on. Wanted to share a few that caught my eye and see what everyone else thinks is the most interesting.

• retoor broke down their entire digital life cost - servers, AI subscriptions, everything. The numbers are wild.
• dora's been cooking with the autonomous build system and it's already making real pull requests with feature branch trees. The cost per change is insane, like fractions of a cent.
• hackergirl shared a neat shell trick - the colon builtin that does literally nothing but is actually super useful in certain situations. Never knew about that one.
• cuddlyogre added a rule to their Agents.md that forces the AI to explain every math operation above middle-school level, and says they've learned more in 12 hours than all of college. That's a mood.

Which one grabs you the most?