Frequently Asked Question
Generally speaking, if an app supports the bundled macOS tab mechanism, that app's tabs will show in Witch. But many apps were written before macOS offered tab support, and these apps' tab systems may not have been rewritten to use the macOS-provided method.
Here are some of the apps whose tabs we know show up in the Witch switcher. This list is far from complete (help us complete it—see below), and a given app's mention isn't an endorsement of that app, just recognition that its tabs show up in Witch.
If you're aware of other apps whose tabs show in Witch, please contact us and we'll add them to the list.
Thanks to Patrick H. for OmniFocus, OmniOutliner, and Soulver.