The basis of the fruity beers is the Belgian beer type lambic - spontaneously fermented beers that are usually matured for another 2-3 years in oak barrels. They are characterised by a sour, fruity aroma with a sharp flavour.
In variants of the classic fruit lambic, you will find cherries, blackcurrants, raspberries, strawberries, peaches or bananas. If you leave out the fruit, it is a gose or geuze. A perfect aperitif!