50501 refers to “Fifty States, Fifty Protests, One Movement” (originally “One Day”). While some states have more presence than others, it has 50 chapters for the 50 states.

I don’t think there’s as much presence on Lemmy, but lots of media gets posted to Reddit at www.reddit.com/r/50501/.

Their website also links to social media accounts covering more of it: www.fiftyfifty.one