Singlebox and WebCatalog are separate apps developed by WebCatalog, Inc.
Singlebox is focused on keeping multiple web apps and accounts together in one compact window. WebCatalog offers a broader app and account management experience, including standalone desktop apps, profiles, and spaces.
The two products also share the same WebCatalog account and subscription system, so you can use the same account and paid plan with both.
You do not need to install or use WebCatalog to use Singlebox. Singlebox works independently and is available at singlebox.app.