I've submitted this 3 years ago but since then a lot has changed in the app - I've added better mobile (and PWA) support and been working on getting rid of the bugs. Direct messages have been added to the chat and the app now handles disconnections more gracefully (although it's still not possible to resume the transfer after a disconnection - this is being worked on).

The app is fully open source: https://github.com/mat-sz/filedrop

This repository also includes installation instructions, and it's very easy to deploy the app with Docker.

Hopefully you will find this as useful as I do (I wouldn't lie by saying that I need to use this at least a few times a week thanks to being an owner of an iPhone).