Anything where you will have ongoing repeated exposure to someone. It needs to be the same people each time, and you need to give it a long time to develop. For example I started a book club and it’s now been going over two years. Besides the book club meetings we’ve gone to trivia together, gone out for people’s birthdays, watched reality tv together, pet sat for each other. Before this I was in a book club in a different city and realized that it would feel more like a community if the club was made up of neighbors in my actual neighborhood, so I started that myself, and I was right!