Video doorbells and home security cameras offer many of the same benefits. Both will show you what is going on outside of your home, both offer motion detection and motion-triggered recording, and in most cases, both let you speak to whoever is out there. That said, the simple fact is that security cameras lack the doorbell component. If you're downstairs doing the laundry and your phone is upstairs, a security camera won't tell you that someone is at the door, but the doorbell will (when pressed).
Signal Private Messenger is one of the most popular privacy chat apps. It features end-to-end encryption for all messages, voice calls, and video chats between two Signal users. It focuses a lot on individual chats. There are group chat features, but it's mostly for personal use. This is one of the biggest differences between it and rival privacy chat app Telegram. Video calls worked fine in our testing so we have no trouble recommending them. It's a neat way to get some encrypted chats as well. The app is also completely free and open source. You can't really go wrong with it, but there are better video chat apps if you need group video chats.