To my understanding it’s mostly a twitter meme pretending to be a philosophy. Basically, the EA people started worrying more about AI risk than about malaria, so some people who think that AI is cool and that there should be more of it took the “Effective” from EA but replaced the “Altruism” by “Accellerationism”. The latter is actually a weird alt right fringe idea by a guy called Nick Land that doesn’t really overlap that much with “Yay tech! Yay AI!”, but the twitter people didn't read it so no matter. And, well, the word sure sounds like “wanting the tech to go faster” so it felt like a nice way to oppose the luddites from EA while hijacking their acronym.

Ofc the “same acronym means 2 opposing standpoints” thing got confusing within hours, so they renamed it to e/acc and there ya go.

There’s nothing particularly effective about e/acc, they only needed the E to annoy the AI doomers.