The late great Jane Grigson has a method for making sorbets which I use a lot. She draws a distinction between granitas and sorbets, the former being the frozen fruit and syrup alone, and the latter being improved by the addition of beaten egg white. You basically make a puree of your chosen fruit, and add sugar syrup to taste (made by boiling together sugar and water) - not too sweet. Then you place this mixture in a shallow tray in your deep freeze, and stir every half an hour or so for 2-3 hours, until you have a thick mush of iced granules. This is the granita stage; you can leave it another hour and it will be a little firmer and ready to turn into a sorbet. Which you do by whisking two egg whites until they're stiff (Grigson suggests using an electric mixer, if possible), and adding the ice a spoonful at a time. This blows up into a lovely foamy mass, which you then refreeze in a larger container until it has the consistency of "firm snow".
Another way of making fruit ices which I love: You freeze your fruit, whatever, and also about the same amount of bananas, in chunks. You then whizz this in the food processor and when it is reduced to breadcrumb-sized bits add some liquid - I often use orange juice, but if you are after a pineapple ice, why not pineapple juice? Or you can use milk or yogurt, or whatever. Go on whizzing, and it suddenly develops the texture of soft ice-cream. Glorious - and you wouldn't think it was fat-free!