Photoshop-compatible plugins fall into several types, distinguishable in Microsoft Windows (and historically in Mac OS 9 and earlier) by their filename extensions.
In modern macOS (from Mac OS X 10.0 Cheetah, onward), all Photoshop plugins are distributed as package folders with an extension of .plugin (or .lrplugin if they are intended for Adobe Lightroom only); the package's Info.plist file includes a CFBundlePackageType code that distinguishes the plugin types, using the same upper-case, four-letter codes originally used in the pre-Mac OS X resource forks; these are generally the same as the Windows extensions but with "M" added to the end (e.g., Windows .8ba = Mac 8BAM).
Many non-Adobe commercial graphics applications also support Photoshop-compatible plugins – Paint Shop Pro,[4] PhotoImpact, and Corel PhotoPaint are some of the better-known ones.
There are several dozen more plugin hosts, including lesser-known products like Chasys Draw IES, the free-software image editor GIMP, and viewers like IrfanView.
Plugins distributed under various licensing models, including "try before buy" commercial software, shareware, limited freemium versions, and "free for personal use" freeware.