The KVS Availability Tool is used to search for flight and seat availability by class, award/upgrade status, route, and date.  It is absolutely invaluable for finding award and upgrade inventory — just the thing to use up those extra frequent flyer miles.  We prefer the Platinum edition which grants access to almost all features for a 'contribution' of $15 for two months (or US$60/year).  The "Diamond" level adds round the world fares and routing routing rules.