Are there any good open source .NET chart components out there that are good for large data plotting and real-time charting? I saw some related topics but they were since 2010 and older, so I'm not sure if they are still valid.
Syncfusion provides a Chart library for all .NET platforms. While not open source, the libraries are available under a community license as well (see details below).
The whole product is available for free through the community license if you qualify (less than 1 million USD in revenue).
Note: I work for Syncfusion.