From Wikipedia: "Japanese animated films and series made specially for release in home video formats without prior showings on television or in theaters, though the first part of an OVA series may be broadcast for promotional purposes. OVA titles were originally made available on VHS, later becoming more popular on LaserDisc and eventually DVD."
This is by no means an exhaustive list, but as a big fan of these strange little things I wanted to gather as many as I could up here. I sourced this by hand from Japanese Wikipedia and on Letterboxd and there are likely to be mistakes because of this. There are also TONS of OVAs that aren't on LB in the first place.
If I should add or remove anything, let me know. Otherwise, I hope this is useful!