I played this card game with my mom back in the 70's. Sometimes we played with more than 2 players. Each player had their own deck of cards. I can't remember exactly how we played, but I think we each had a pile of cards to play from in front of us face down (maybe 21 cards in stack/pile but not sure). There were 4 slots/piles to play from/on on. 4 piles were either beside our playing stack or in front of each of us. I also think there was a pile/base/stack of cards in the middle face down. I don't remember if we had cards in our hands or not.
The descriptions sound a little like a game I played at school and was know by us (possible as local dialect) as Slam.
Doing a google search I've found [double patience] which matched your description.1
28 cards are played out in 7 piles with 1-7 in each (if you recalled 21 then then would work as 6 piles 1-6 in each)
The object is to get rid of your cards onto central piles.
It's possible to play with multiple players if each player has their own deck.