Ask HN: Recommendations for open source Framework/Library to work on

I'm a CS student who just finished his second year in school.

I'm passionate about Data Science, Visualizations, and cool web technology. I have a large background in development. I've never worked on a open source project and want to give it a shot!

Does anyone know of any projects that are cool? I've been looking and thought I'd ask the HN community.

Thanks!