I have made a journey recorder which I use to record my public transport journeys on the go. However, a significant portion of my journeys are in places without internet access, such as the Underground, which make me difficult to use it and sometimes I have to resort to a notebook and entering it afterwards.
If the web app can be made to work offline, the problem can be solved. I have made a new test version (1.6.0-beta.1) which can be loaded offline using a service worker, and the submit buttons are disabled while the device is offline.
Try it out at https://journey.miklcct.com/ on your own database, or deploy your own copy from source for production use.