There are channels and plugins are which are offered through the Unsupported Appstore, by direct download from GitHub, or via links in the forum. These channels either haven't been reviewed for inclusion in the Plex Channel Directory, are considered less stable and harder to maintain, or contain content that may be considered offensive or questionable. These channels may have more extensive coding or require a lot more user support. Since these channels may be more likely to have issues, require special instructions and/or be more difficult to maintain, they are usually only maintained and updated by the original channel creator.
Unsupported Appstore v2
There is one channel available on the forum, which acts as an unofficial directory of some channels. This Unsupported Appstore (UASv2) provides easy access to a wide variety of channels which are not available via the official channel directory.
Some enterprising users have noticed that most channel developers post their code to GitHub and choose to download channels directly from there.