I'm u/therealkurumi2 on Reddit, where I've written (so far) 99 flash fiction tales of science fiction and horror; see the full list. All are 500 words or shorter.
My first story collection is published (e-book only at the moment): Young Man, Open Your Winter Eye. Included are longer tales, including a 16,000-word novella with that title.
As a bonus just for readers like you, here's a 1000+ word tale that never really worked as 500 words, and was never submitted. It's called My New Old Friend.