iRegatta Flags is an overview of the maritime signal flags from A-Z, number flags, the substitute pennants and the answering pennant.
You can tab on any letter flag and see what they mean according to the "International Code of Signal".
A separate section describes how the flags are use in sailing regattas. You can see how the race committee signals the starting procedure, early starts, postponements and race abandonment.
The "Rule book" section has quotes from ISAF's "Racing Rules of Sailing 2009-2012" that relate to the flags for the start procedure and the shortened course.