Redpill

Redpill (also known as RP) is a licensing system used by early builds of Windows 8 to restrict access to certain new features of the operating system, including the Start screen, the redesigned login screen and OOBE, the ribbon UI for Windows Explorer, a new theme, and the execution of WinRT applications. This system was implemented to prevent those features from being usable in leaked builds of the operating system.

Redpill depends on certain licensing policies to be installed. If those licensing policies are not present, the UI generally resembles Windows 7 with all of the restricted features being missing. However, when those licensing policies are installed, the build begins to check for the presence of some registry keys which enables or disables Redpill. Finally, the Shell Side By Side library (shsxs.dll) is loaded, which contains certain assets and code patterns used by some of those new features. With all of these present, the features are available.

The first known build to use Redpill is build 7850 and the last known build to use it is build 8121, with newer builds having all of the new features be enabled out of the box.

Implementations
There are several applications developed to enable the missing features.

Original Microsoft Implementation
The original Redpill depended on the product key you entered in during Windows Setup. If the key is for a license that allows Redpill, Windows Setup would download the Redpill tool from an internal Microsoft server. The tool will install the licensing policies appropriate for the product key used, some registry keys, some certificates, a manifest used by the System Reset feature and shsxs.dll. When run on newer builds, the Immersive Browser is also enabled via DISM.

Windows 8 build 8102 was distributed with the Redpill installed, allowing for all of the new features to be usable out of the box. As of 2020, the original Redpill tool is unleaked. But, the files and policies found in build 8102 helped led to some of the third party implementations of the Redpill to be created.

RedPill Enabler
RedPill Enabler (also known as the MDL Redpill Enabler after the forum where it was first published on) was the one of the first public applications meant to enable features restricted by Redpill. It was developed by Vizion, a member of the My Digital Life forum, and was initially released on 2011-06-17.

It works by replacing slc.dll, the Software Licensing Client DLL, with a modified one that has some of the features enabled, such as the Windows Explorer ribbon and the new theme. It also includes a set of icons for the ribbon explorer to replace the placeholder ones that some builds used and a copy of the new Task Manager from build 7971. It also allowed for the tool to be integrated onto a build's install.wim file.

The tool is heavily criticized for the limited amount of features it unlocks, it's method of unlocking said features, and it's success rate, with some people reporting multiple features and functions of a build being broken after running this tool.

Metro Unlocker
Metro Unlocker (also known as MetroUnlocker or simply MU) is a tool developed by MetroFetro, a YouTuber and developer. It was the first public application that allowed for all restricted features to be enabled, including the Start screen, and remained the only application to do this from its initial release in 2016 until the release of Redlock in 2020.

The first version, released on 2016-01-03, only supported build 8056, and worked by disabling the Software Protection Service, the Windows service responsible for Windows licensing, and importing in the licensing policies from build 8102, which included the policies needed for Redpill. It also dropped a modified version of 8102's shsxs.dll. Version 2, released on 2019-03-15, added the ability to "enable" the Immersive Browser by importing in the files and registry entries for it from build 8102. Version 3, released on 2019-05-10, used the Immersive Browser files for 8056, along with adding in support for builds 8032 and 7989. The latest version, version 4 released on 2019-08-05, dynamically writes in the RP policies instead of overwriting all policies with the ones from 8102, introduced a slc.dll hack to enable the Immersive Control Panel's personalization settings for build 8056, and introduced support for builds 7927 to 8056.

The tool is heavily criticized for its method of installing the RP policies in earlier versions, its use of a registry and file drop method for enabling the Immersive Browser instead of using DISM to do so (the way that was intended by Microsoft and was used with 8102) which also initially used 8102's files instead of 8056's, its use of a slc.dll hack to enable the personalization settings instead of a policy modification, and perceived laziness with the modifications to shsxs.dll.

Redlock
Redlock is a tool developed by lucasm and gus33000, two BetaWiki members and software developers. The initial version was released on 2020-01-29. The tool is designed to replicate Microsoft's original Redpill implementation as possible.

While it does disable the Software Protection Service like Metro Unlocker, unlike Metro Unlocker, it dynamically generates the shsxs.dll file for the specific build (instead of using a modified copy of 8102's shsxs.dll file). It writes the same policies, certificates, manifests and registry keys as the original Redpill, along with using DISM to install the Immersive Browser. It also includes a modified version of the 8102 pattern designed to work properly with the builds that look for pattern data from shsxs.dll.

Compared to the previous third party tools, Redlock has been praised for its compact size, stability, speed, and cleaner method of enabling the features.