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MahApps.Metro
A framework that allows developers to cobble together a better UI for their own WPF applications with minimal effort.
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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.
WPF can be made a lot more modern looking with free open source libraries. For example https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit Most libraries and projects work well with it, which may put it ahead of WinUI if they aren't updated yet.
https://github.com/MahApps/MahApps.Metro is another good one.
NOTE:
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Hence, a higher number means a more popular project.