Application Based Firewall
A common question asked by Windows users new to Linux is how to block applications from accessing the web. To stop phone home nonsense. The simple answer is there are no user friendly GUI apps to provide that service.
The geeks thump their chests and start spouting iptable rules, which make the eyes glaze for most users. Moreso, iptables is not designed to block outgoing packets by specific apps.
Die-hards argue that no such app is needed.
Proprietary software is available for Linux. Despite an otherwise high level of trust, sometimes distro maintainers need to be blocked as the Ubuntu folks demonstrated when they decided to share search data with Amazon. (How similar to the Windows XP file manager phoning home with search data.) That specific Ubuntu feature no longer is the default but remains available and could be inadvertently or maliciously changed.
Yes, an application based firewall tool would be useful. The Microsoft and Android folks have proven that.