I am working on MagicBell because it's a problem faced universally by B2B apps, and one I have experienced personally at my last company - SupportBee, a shared inbox product.
There, we deliver over a million notifications a month to our users. Before MagicBell, we spent a significant amount of time writing code to figure out whom to notify (based on the activity and their preferences), delivering the notification via email, and providing customer support when it wasn't delivered timely. When our users asked for an in-app notification center and mobile push notifications, we realized that we'd have to do a lot more work, especially if we wanted to avoid duplicates across channels. We talked to other companies at our scale and validated that they struggle with this problem too.
Instead of solving this problem just for SupportBee, we decided to build MagicBell.