Ask HN: Most exciting open source projects to contribute to?

I've been looking to give some time to an open source project, but have been away from the development world for close to 5 years. Looking for a project to work on that includes the following:

1. Working on solving an interesting problem, something meaningful for the world. 2. Easily accessible. Low barriers to hopping on board and getting started. 3. Great community of people that are wonderful to work with.

Thank you!