Short answer
What is the best free break reminder for Mac?
Time Out is the safest free starting point for most Mac users because it
is mature and highly configurable. Stretchly and BreakTimer are better
if open source and cross-platform support matter. Peeku is the pick if
you want a Mac menu-bar coach with local presence signals, eye breaks,
walk reminders, posture and distance nudges, and no account.
Choose Time Out if you want normal breaks, micro breaks, custom themes, actions, scripts, and optional activity charts.
Choose Stretchly or BreakTimer if you want free open-source software across macOS, Windows, and Linux.
Choose Peeku Presence Coach if you want Mac-specific local presence context, private desk-health nudges, and an optional screen-saver-based walk-away lock in the menu bar.