The Staten Island Ferry (referred to as "Ferry" in the rest of this
writeup) connects northern
Staten Island with the southern tip of
Manhattan. A one-way
trip takes approx. 30 minutes. All Ferryboats are passenger, and about half can carry cars as well. All boats are fully-covered and
heated/
air-conditioned, so are
comfortable year-round. Each boat has a
capacity of several
thousand.
The Ferry runs 24 hours a day, 7 days a week. There's a set schedule, which has Ferry runs as frequently as every 15 minutes (during morning and evening rush hours), and as sparse as every hour (during overnight hours and weekend mornings).
There are two main types of Ferryboats. The older Kennedy-class ships can carry cars, as well as passengers. This allows those who want to drive from Staten Island to Manhattan (or the opposite direction) to go on the boat, and not have to drive through Brooklyn or New Jersey (there are not any roadways that directly connect Staten Island and Manhattan). Seats on the Kennedy boats are hard wooden benches.
The other type of boat, the Newhouse-class ships, are newer, but can not carry cars. Seats are individual multicolored plastic (I think?).
Overnight, there's a smaller ship (possibly two. I don't travel at night very much) that looks like a Kennedy ship, but doesn't carry cars I don't believe.
The Ferry is free, and is popular with tourists, as it passes The Statue of Liberty and is ideal for pictures. It's also the method of transportation for a large number of Staten Islanders (including myself) who work in Manhattan. Wall Street and the World Trade Center are within walking distance of the Manhattan terminal.
At both Ferry terminals, there's connections to subway/train and buses, as well as taxis.
The Ferry has been immortalized in the movie Working Girl (why did I originally think Pretty Woman?) and also in the opening montage of Late Show with David Letterman.