Photopea, it's a web based photo editor that is really really great. If you install it as a PWA, it works offline. Similarly, excalidraw, monkeytype, google calendar all work offline if you install it as a PWA.

Apart from that, I have youtube music, slack, discord, whatsapp web just for convenience of having it in alt+tab rather than cycle through a thousand tabs (admittedly, this usecase is nullified by tab search)