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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
Nullpomino is pretty good for what you're looking for. It's lightweight but requires a bit of setup first - scroll down to the Download section, download and run the installer, and you might have to download some other stuff the program depends on. It's a bit confusing at first, but once you figure out how the menus work there's a ton of game modes to mess around with. I don't think it can be set to hover over all your windows, but it will autopause if you click on something else.
Cambridge. It has a wide amount of customization and ability to add your own modes. Plus, it's very lightweight and doesn't require Java Desktop.