Übersicht lets you run system commands and display their output on your desktop in HTML5 widgets. The widgets are easy to write, customize, can show data in tables, charts, graphs, and more. The widgets are also responsive and are able to resize dependent on the screen dimensions.
GeekTool is similar to Übersicht in some ways, but limited to four categories of widgets to display: File, Shell, Image, and Web. The Dark Sky weather widget is popular. Users comment that it chokes on Mojave and more recent MacOS releases have left some features unavailable. There's a community sharing tips n' tricks over at: reddit.com/r/GeekTool/
Both suffer from a similar lack of updates which is surprising considering the popularity of Rainmeter on the Windows/PC platform.
Image credit u/hassanazzam95