Thinking of how to translate "App Tab" in Ukrainian, one idea surfaced:
taking the meaning of "App" as "an app is often a self-contained
environment for performing some well-defined task" we (Ukrainian l10n
team) found that "Purposed Tab" describes the thing pretty well.
"Purposed" distinguishes it from other tabs, and explains why it may be
different inside - it is not the general tab, but a tab that is tailored
for some specific task/site.
Hope that helps other localizers.