|Wikipedia has more information about Monaco (typeface).|
Monaco was one of the original Macintosh "city" fonts by Susan Kare. It is a monospaced sans-serif face. The TrueType version is still popular with programmers today, as several often-confused character pairs are easily distinguishable – notably the subtle difference between O and 0.
A somewhat modified version of Monaco was used in the final two installments of the Marathon Trilogy; Marathon 2: Durandal, and Marathon Infinity
Montagel is a look-alike with identical metrics.