My first experience roleplaying was on some website I found that I can't even remember the name of. It was an original fantasy setting and it had a map. Clicking on a location on the map would "go" to that location, and there would be a chat room where everyone at the location could talk. Then you could navigate to nearby zones/areas/places/buildings, and the chat room would change to that area. It was very neat and very fun, but I had no idea what I was doing.
A major part of my RP past was in Neverwinter Nights, a PC video game based on D&D. Very good game, 10/10. You could play online, and there were tons of RP servers. I played on one called Astoria, an original D&D world, as... a 12-year-old "human" kid. Since you cannot control height in the game, I made my character a halfling and told everyone I was a human. After several years of playing, I asked the GMs to change my character data to look like a human, and they did and it was awesome. My character was the strongest monk(played more like a fighter/brawler. Limited "spiritual" training, and such) on the server but was only level 9. I helped slay Skrag, an ancient red dragon that attacked the main city of Astoria. I was one of the "core" people from Astoria. There were several core groups as the server was fairly large. There was a vampire/drow populous that caused a ruckus from time to time, and then there was an elven city which had a bunch of races, but mostly elves. People tended to stay in their areas mostly because they knew lots of people there. The coastal city of Astoria was my character's home.
Then I found Warcraft 3 and never RPed in an online game again because I was too busy killin' shit. Mostly. In the last 12 years, any online RP I've done has been limited to one-off random events. I tried leveling a character on an RP server in WoW a long time ago but just wasn't into it because it was difficult to make RP the main attraction.
That said, I do play tabletop games, and I have not played in over a year now, but I my favorite one is Savage Worlds. I am very well versed in Pathfinder, D&D 3, 3.5, 4, and 5.
Oh, and as far as forum based RP goes, this website is the first time I've ever done anything like it, aside from that chatroom based website I mentioned.