Oh, definitely not a purchase, but Emacs. My life was a mess because of Twitter and it was anti-Twitter in every way – no characters limit, offline, insanely powerful. While Twitter would prevent me from prioritizing, Org-mode could handle task lists, spreadsheets, text documents, with academic citations support, and could export them to .ics, .odt, .pdf, .md, etc. Ideas are affordances and Emacs has let me focus on these instead of trying to build a picture perfect online profile.

Whereas Twitter isn't meant for most people's use cases so it runs a long-term scam called “optimization for engagement” (which is actually abuse by definition), doing everything it can to prevent its victims from taking hindsight on and conceptualizing what's happening to them, Emacs is letting me channel all of this frustration into reading and writing my master thesis. Which deals with how social media increase social inequalities. Highly recommended.