Roll20 has just released their most recent usage report and the numbers are interesting, at least as far as Old School Gaming goes.
But before we get to that, note that there are over 18k D&D 5e games listed and a hair under 22k players expressing interest in 5e - which should indicate an abundance of 5e games with room for players, which isn't the results I've heard.
Now lets look at AD&D. While only 1.59% (730 games) of the games listed on Roll20 are AD&D, 9.62% or 4,556 players express an interest in AD&D. That's nearly 1 in 10 players on Roll20.
Stars Without Number has 598 games and over 1,300 players. Basic Fantasy RPG has 432 games and over 1,110 players. OD&D has 193 games and over 1,600 players. DCC RPG has 75 games and nearly 400 players. Labyrinth Lord and Swords & Wizardry have 41 games each and 144 / 182 players respectively. Castles Crusades has 25 games and 124 players. This isn't even touching upon games like the Palladium System, Traveller, Warhammer, Hackmaster, CoC, RuneQuest, Rolemaster and the like.
Just looking at the number of games (as players can and do identify with more than one system, so those numbers will add up to over 100%) shows how strong Old School Gaming is on the Roll20 VTT platform.
About The Orr Group Industry Report
We pull our data from two locations within Roll20 member profiles. Player numbers are drawn from the “Enjoys Playing” and “Seeks Group For” sections, while Game numbers come from the “My Campaigns” section. Our percentages can total more than 100%, particularly Player numbers, since each player will list their interest in multiple games. The report is meant to be a representative sample, and the game listings are curated by Roll20 staff.