Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Bashupload - Upload files from command line to share between servers
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.
FilePizza - Open source application used to transfer file via WebRTC and WebTorrent.
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.
BlackHole File Transfer - Blockchain-based file transfer. Designed for everyday use.