"Regional Multiple Listing Service (RMLS™) is the Northwest’s largest REALTOR®-owned multiple listing service, serving approximately 11,900 real estate professionals in over 2,400 offices throughout Oregon and Southern Washington. The RMLS™ database holds an archive of over 1.6 million listings, including about 25,500 active listings (plus or minus depending on the season), and over two million tax records."
"The RMLSweb system—used by REALTORS®—is developed in-house by our programming staff." RMLS is one of the few, maybe the last MLS that makes its own MLS software rather than buying it from the dozen or so MLS software companies.
See attached county list, and here is some history from the MLS website: "In the beginning, RMLS™ served only the five-county Portland metropolitan area in Oregon. The Douglas County Board of REALTORS® initiated discussions with RMLS™ early in 1998 to see if service could be extended to that area. Service to both Douglas and Coos Counties in Oregon was added later that year. The following year a merger with the Clark County, Washington MLS was finalized, bringing membership over the 7,000 mark. Service to Lane County followed in 2001. Curry County and the Mid-Columbia region in Oregon and Washington joined in 2005, with the Columbia Basin and Baker and Union Counties following suit in 2007 and Wallowa County in 2008."