When Boeing launched the 737NG family, the original models were very similar in size to the previous generation of 737s.  However, there was pressure for more capacity so they added a new model to the family with the 737-900.  A few were sold but it was not a capable enough aircraft and hardly anyone bought any.  Instead, Boeing had to redesign the aircraft with some more capacity after redesigning the rear bulkhead and some more range resulting in the 737-900ER.  This has sold considerably better.  There are still a few -900s around though and Alaska has a few.  They are very early jets and they are not worth the investment for adding winglets so they are some of the few NG generation jets to still have wings with the original wingtips.  Here is one of them arriving at Paine Field.