B4A is only one part of the whole B4X suite which does support, next to Android, also other platforms like iOS, MacOS, Windows, Linux, Raspberry Pi, Arduino and Web applications. The business logic is almost 100% compatible between the platforms, and with the recent addition of XUI, most of the UI layout too.
Its basic-like language is very easy for beginners, and the possibility to write plugins/libraries yourself gives power users the ability to extend its possibilities.
B4A has a strong, active and friendly community (96K+ members at the point of writing) and they contribute a lot of free libraries.
One of the most unique features of the tool is the possibility to live code swapping in debug mode. This allows you to change code while running on a real device without having to recompile. This feature alone puts it miles ahead of the competition regarding productivity.
The developer of B4A himself is very active and accessible on the forum. Updates (bug fixes, but new features too) are fast, sometimes within hours.
The uses for this tool are very versatile: from games over IoT to large CRM applications.
Time and job management (android & desktop)
Enterprise Web development tools
It has been a huge time (and money) saver over the years