A Betta will build a bubble nest when it is happy. When Bettas have babies, the male picks up the eggs in his mouth and sticks them to his bubble nest so he wont lose them. The babies hatch, and they cant swim until they absorb their yolk sacks because they are too heavy, so they hang out, stuck to the bubble nest. Bubble nests also attract females. A nice nest is like a new BMW. The bigger and frothier the nest, the more interested a female will be because her babies will be safer.
I have had all kinds of anabantids but have only ever seen a betta make a nest. They breathe in air from the surface, go an inch under water, and blow out bubbles into specific locations to make a uniform nest. They breathe and blow like this about 20 times a minute and its great to watch.