Windows Sidebar

Windows Sidebar is a component of Microsoft Windows. It allows the user to place multiple gadgets that could show information such as time, weather, calendar, and system resources use in a vertical bar at one side of the desktop, as well as other downloadable ones. It was first introduced in Windows Longhorn build 3683 as an addition to  and was last seen in early builds of Windows 7 before being replaced by a similar gadget app.

Pre-reset Windows Longhorn/Vista
Windows Sidebar was one of the features introduced in Windows Longhorn. Its assemblies was found in, together with other Avalon-based shell features. Build 3683 is the earliest to contain it. While it's disabled by default, it can be enabled from the Taskbar and Start Menu Properties menu. Its default position is the desktop's right side, but it could be moved to the left side. It could also be combined with the taskbar, a feature that made it disappear while its items were moved to the Sidebar. Although there are no tiles pinned at first, they can easily be added from the context menu's "Add a Tile" option. As development progressed, more changes were introduced, such as a new taskbar with the Sidebar integrated to it, new or changed tiles, and appearance retouches.

For most of the development, the Sidebar used the Plex-like blue and the light gray from the Windows Classic theme as its only color schemes. The private M5-M6 Aero theme used a black Sidebar instead of the normal blue one. However, with the arrival of Milestone 7 build 4042 (Lab06_n) and the Slate theme in replacement of Plex, the Sidebar was updated to reflect this change, now featuring a darker gray as its predominant color. Build 4066 introduces the Aero-style sidebar. While the enabling procedure is identical to build 4074, the sidebar is hardcoded to use the Slate-style one, requiring the  assembly to be patched, removing the hardcode. Since build 4074, the hardcode has been removed permanently, thus only requiring a theme file called  to be used to enable the transparent Aero-style sidebar.

On several builds, particularly after build 4015,  is very unstable and often causes memory leaks. This is often because of the Sidebar which runs on it, meaning that it must be disabled to reduce their effects. While this problem disappeared for some time, chances of experiencing Explorer problems in general increased again with final builds such as those from the 408x line and build 4093.

Post-reset Windows Longhorn/Vista
Early builds compiled after the development reset of Longhorn had a more similar functionality to Windows XP, and thus didn't have any features from the pre-reset project implemented yet. While Beta 1 builds already contained some Longhorn features, the Sidebar still wasn't present, and the earliest available build to contain it was build 5212. This time, the Sidebar was running on its own process,, instead of  , a change that was intended to reduce memory leaks and instabilities from the Longhorn project. This Sidebar also lost some of its previous capabilities, such as being combined with the taskbar, and most of its previous tiles, which by this point had been renamed to gadgets. In build 5342, some additional tiles were added, but none of them were from Longhorn.

Since the first build, the Sidebar had a design reminiscent from late builds of Longhorn, being a transparent black bar, although the color's opacity was decreased in this case. In later builds, the black color was removed, leaving a fully transparent bar that now only appeared when the cursor was placed over the Sidebar's area. Otherwise, a dark shadow would appear on its place.

Replacement
While the Sidebar was from a few changes that survived to the Longhorn development reset, it was quickly replaced in Windows 7 build 6519 with Desktop Gadget Gallery, a similar feature that allowed gadgets to be placed anywhere on the desktop, rather than just on a bar, and gave them independent customization options. Desktop Gadget Gallery, however, would run the same fate as Windows Sidebar since it was discontinued in Windows 8 due to security risks.