Usage Monitor checks on a regular basis which application is in the foreground and stores this information in its database. It can visualize the historic information thus obtained in different ways, in order to give you some impression how you spent your time at your Mac.
The application icon was donated by Steffi Winkler.
The only known way of obtaining Usage Monitor is to download it from here. (Decompress it using a ZIP utility like the "Archive Utility" of Mac OS X or the "StuffIt Expander".)
The source code is available here, so you can check that the program does not try to raid your refrigerator.
If you do not want to use Usage Monitor anymore, you might want to delete its database. You can do so by deleting ~/Library/Containers/Jakob.Usage-Monitor. (If you are curious: The database files are in ~/Library/Containers/Jakob.Usage-Monitor/Data/Library/Application Support/Usage Monitor/.)
Usage Monitor is working only when it is running. If you do not want to have to start it manually each time you want to collect data, then you can register it as a "Login Item" (should be "log-in", by the way, as the noun made from the verb "log in") in the macOS System Preferences, section "Users & Groups". After that, it will be automatically started each time you log on.
The period of the measurements, by default one second, can be adjusted in the preferences. When Usage Monitor is running in the background on my MacBooks, the CPU consumption is negligible if the period is 2 s, and it is around 0.2 % with a period of 1 s.
The menu item Show Statistics opens a window showing the bundle IDs of applications and the estimated time these applications spent in the foreground during the time range determined by the date pickers at the top of the window. "Uptime" is the total time Usage Monitor was running in this time range.
The button Graph in this window does the same as the menu item Show Graph, which opens a window displaying graphs for the usage of the applications selected in the list of the statistics window. The time range between the dates determined by the date pickers at the top is partitioned into a number of sections determined by the text field , and the graphs show the average relative usage time of the respective applications for these time intervals.
If you choose nonsensical time values, Usage Monitor does nothing but beep at you.
You can zoom in by selecting a time range with the mouse, dragging from the start of the new time range to its end.
The item Database opens a window for database information and maintenance.
If you want certain applications not to be recorded, you can select the respective rows in the statistics window and give the Delete command of the Edit menu. This will also delete existing historical entries for these applications from the database.
The preferences of Usage Monitor contain a list of the applications banned in this sense. You can remove applications from the banned set by deleting them from this list.
It is now the more intuitive number of sections rather then the resolution that can be configured in the graph window.