Air Quality Index (almost everyone I know uses this, but I'm in a more polluted part of the world).
Some internal company ones giving quick KPI/dashboarding. I think this market is under-served by corporate apps in general. If a process is critical to an organisation no matter it's size, a widget can be a great tool for monitoring it.
When a real-time statistic is sufficiently important I prefer a widget to needing to load (or even develop) a dedicated app. I can then go through unified web-based (responsive) interface to take any action needed.