iStat Menus 6
Notifications, based on CPU, network, disk, battery, weather and other events.
Hotkeys to open and close menu dropdowns, for quick keyboard access.
Reorderable dropdown menus, with the ability to hide sections.
A compact Notification Center widget, covering some of the popular iStat Menus features.
There are more changes, including an indicator for AirPods battery level, though I already get that through Tooth Fairy. Also interesting is that it can show weather information, and that this is enabled by a subscription fee ($6/year for 15-minute updates).
Update (2017-09-26): See also: MacRumors.
Update (2017-09-29): See also: David Sparks and Agen G. N. Schmitz.