Unreleased neighborhoods

There have been several neighborhoods made by Maxis and Electronic Arts for The Sims 2, The Sims 3 and The Sims 4 that were never released to the public. Riverside and Waterside were used in previews for the pre-released The Sims 2 but never released, and a third neighborhood named Sedona is referenced in game files. Two versions of Sunset Valley were made but due to the delay of the release of The Sims 3, additional changes were made.

Riverside
Riverside was originally set to come with The Sims 2 base game, but many changes caused it to be removed. There is a high speculation that families in the various previews may have been the inhabitants of Riverside. It can also be seen that the template for custom Pleasantview and Riverside are the same, hinting that Riverside was renamed Pleasantview, and had most of the lots and families removed.

A recreation of Riverside has been attempted by Thsms204, but was later cancelled in February 2010. Another group, called "The Riverside Group", attempted and completed the recreation of Riverside in March 2014, available here.

Waterside
Waterside was a neighborhood used for previews of The Sims 2. It was founded by Tim LeTourneau. It was originally set to come with The Sims 2 base game, but many changes caused it to be removed. It is the assumed home of various Sims including Dina, Laura, and Tina (all past girlfriends of Don Baxter). It is known to be the home of the Baxters, Virginia, and many other relatives to the Baxters. Oddly the neighborhood description for Waterside remains in the neighborhood manager files, though unlike Riverside text is missing. Waterside also has some lots that can be found in the Lots and Houses bin, as the Cape Cod Classic and 225 Main Street in Pleasantview can be seen in the picture above. A recreation of Waterside had been attempted by GPKman. Mate1234 is now starting his own recreation.

Waterside's description revolves around the key family in the neighborhood, the Baxters.

"Don, Sarah, and little Alex settled down in Waterside. Sarah wants a bigger family, but Don still craves the romance of his youth. Can you hold this family together, or will these Sims just grow apart?"

Sedona
A neighborhood named Sedona is referenced in the neighborhood manager, however the file is text-less and it was not featured in any previews for The Sims 2 so details are scarce. It is likely associated with the neighborhood template Sedona. In Lucky Palms, a world in The Sims 3, there is a street named Sedona Lane. This could be a reference to the unreleased neighborhood, since both neighborhoods are in the desert.

It can also be speculated that these were intended to be the released neighborhoods; that Riverside and Waterside would be Pleasantview and Veronaville, and Sedona would be Strangetown. A recreation of Sedona was attempted by ParanormalJ and Venus Creations separately, but both were never finished. A group named "Hood Building Group" at MTS, attempted and completed their recreation of Sedona in August 2015, available here.

Unused flythroughs
Hidden within the game are a number of neighborhood camera flythroughs that are not used, but are still associated to specific neighborhood names. It is possible to enable these for use for any neighborhood by simply renaming it to one of the following:
 * Sedona
 * Europa
 * Lakeview

As the flythroughs follow pre-determined coordinates, a neighbourhood's terrain may not be ideal for them. The camera might clip through terrain and lots.

The Sims 3
Even though Sunset Valley was shipped with the game, two versions were made but never released. The first version was made in March 2008 but was revamped. Then the second was made after that and was supposed to release in February 2009 but was delayed.

Windenbourg
In early screenshots of The Sims 4 there was a world that seemed to be a prototype of Get Together's Windenburg. The game's files referred to this town as Windenbourg. The concept of this unreleased beta world was reused when creating Windenburg.

Rose Beach
Shared concept art of The Sims 4 reveals a conceptual, coastal beach world called Rose Beach. It features a large beach, a cave entry and expensive houses on top of the cliffs.