Uptil 1998 the US used to make their 25¢ coin the famous quarter in one design only. Then by an act of Congress since 1999 they started issuing 5 quarters every year with a unique design on each, in this case commemorating each of the US states in ascending order of their joining the US. This was called the
50 State Quarters® programme [complete with the ® mark;-)] At the rate of 5 per year they ran through the various states by 2008. However earlier on the people of Washington DC protested or requested that they too be accepted in the programme. The US Mint agreed for this and so in 2009 DC, Puerto Rico, Guam, American Samoa, The U.S. Virgin Islands and The Northern Mariana Islands where added. No no they are not US states at all, and I don't think they protest/requested but it made a nice 5 coin set.
Very obviously the US Mint found this entire programme very profitable. Why do I say so? I am saying so since they are now introducing the National Sites Quarters Program -
America the Beautiful Quarters™ [Yes with the ™ mark] They start issuing from year 2010 at the rate of a nice 5 coin set BUT in 2021 they have only one coin being issued. Hopefully by then someone might protest/request 4 other sites to be added;-)
Since about 2007 they started issuing the US President dollar coins called the
The Presidential $1 Coins [no ™ or ® mark for this] this was in addition to the Sacagawea 1$ coin that they started issuing since 2000. For now this programme runs till 2016 with Gerald Ford. Since this is in the order in which they served [and not died] Carter, Reagan, Bush Sr, Clinton, Bush Jr and Obama will join it regardless.
Maybe someone from the Franklin Mint joined the US Mint in 1999;-)