Annotate PDFs right in the browser — add text, draw freehand, stamp a signature or image, then download. Fully client-side; your files never leave the page.
Tools.
Small utilities — most run entirely in your browser.
Split expenses with friends and settle up — a self-hosted Splitwise. Sign in with Google, add friends as names, log expenses with equal/exact/percent/share splits, and get the minimal set of payments to square up.