Bashupload - Upload files from command line to share between servers
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
FilePizza - Open source application used to transfer file via WebRTC and WebTorrent.
Xamarin.Android - Integrated environment for building not only native Android but iOS and Windows apps too.
BlackHole File Transfer - Blockchain-based file transfer. Designed for everyday use.
Kodular - Much more than a modern app creator without coding