Steamer, Zips, Bill James, PECOTA are all projection systems. Fangraphs does not do projections - they list other people's. They are all about the same in regards to their methodology with some minor differences. Like other projection systems, Steamer uses past performance and aging trends to develop a future projection for players. It also uses pitch-tracking data to help forecast pitchers. On Fangraphs, the projections are updated daily and predict each player's numbers over the course of the remainder of the season. Obviously, no one is claiming that every one of Steamer's predictions will come true, but it is widely regarded as one of the most accurate predictors in the industry. http://m.mlb.com/glossary/projection-systems/steamer