Commuter trains in Jakarta connect the city center with outlying regions, namely Tangerang, Bekasi, Depok, Bojonggede, Bogor and Serpong. Commuter services operate from 5 a.m. (first train departing Bogor to Jakarta) to almost 10 p.m. (last train leaving Jakarta for Bogor). Trains often run late, though. Weekend special services connect Depok and Bogor with the popular Ancol entertainment park in Jakarta.
Several express trains (and semi-express trains) stop at other stations only at certain times outside the rush hours. All trains other than the expresses do not stop at Gambir station, the main station in Jakarta, so this might be a problem for those arriving from other regions and wanting to continue to other stations. The choice is to take an express train to the nearest station and continuing by other forms of transport, or taking a taxi to Juanda station, located a few hundred meters north of Gambir, close enough if you wish to walk.
There are four types of trains: express (air-conditioned non-stop trains, generally most useful for commuters going and returning from work), semi-express (similar to express, but with more stops, runs outside the rush hours), ekonomi AC (all-stops, air-conditioned, probably most useful for tourists) and ekonomi.
Riding the ekonomi class is not advisable: crime and sexual harassment are known to happen inside packed trains. During the non-rush hours, though, economy train travel is quite an interesting experience. It is a tour of Jakarta's darker side, with peddlers offering every imaginable article (from safety pins to cell-phone starter kits), various sorts of entertainment, ranging from one-person orchestras to full-sized bands, and a chance to sample real poverty; you are riding a slum on wheels.