Oh wait, I still play Doom which I got in 1994. Does that count?
The first Doom was the best and it came with a map editor which I and most others used. What other game ever changed everything like that. I cant say I use the game but modern CS is based off some quake 2 code which owes something to Doom I guess.
windows apps dont really count I guess. Start>run>iexplore is still in windows and used by me, first use 1997
Yahoo website is still useful and this forum also, I got the AMD pencil trick kit back in 2000 with 50 gram aluminium heatsink and 20mm fan

FT.com might the oldest site I think of Ive used irregularly or BBC and CNN I think also all active 1997 to now
This guy is a bit of a legend, again he has been around for years and was active in the 90's till now -
https://www.grc.com/resume.htm
Oldest game, multiplayer with hundreds of people back in the 90's was a big deal. Still going now, you might think hows that possible it was and is text based via telnet protocol predating html

The owner is a VP with a major company in NYC apparently, he spent a lot on hosting bills back in the day for sure. -
https://muds.fandom.com/wiki/Avatar_MUD
Must be others, cant think of them. X-com ?
Stuntcarracer, google that right now still a great game and will run, circa 1989 I wish they made a sequel like Elite has now but nope, the original still conveys its great physcs from a unique genius programmer Geoff Crammond I recommend giving it at least 1 lap try.