This is the most common form of "owning" apartments and other housing where you benefit from having common infrastructure like heating and water.
"Bostadsrätt" in Swedish, Google translates the wiki page quite well. https://sv.m.wikipedia.org/wiki/Bostadsrätt
It seems like a good way of keeping investors from buying apartments and only allowing people in who are going to live in them. Better then nothing, but honestly I prefer the way it is done in say Germany. The co-op buys the building and everybody can become a member for a reasonable price. Then you are allowed to rent the apartment from the co-op, which pays the mortgage, utilities and other costs of the building. Anything left over is return to the members, which is meant to be nothing. Thanks to scale and time this means lower rents. Especially when the mortage is paid off. However you do not really built up wealth this way.
Due to other dysfunctions of the Swedish housing market, it's not exactly making housing affordable. Far from it, the housing coop market is mostly inaccessible to people without significant starting capital for a down payment on a mortgage. With the increased interest rates, they are also not particularly cheap in ongoing mortgage costs either.
True, thanks for clarifying this. But it does help to keep the utilites costs of the houses at actual cost, because the houses are co-owned and non-profit. It is also keeping out private speculation and "landlords" from the market with how the statues/rules are setup.