gistfile1.txt

A note taking app...lol, i know what youre thinking....hear me out.... with a focus on a timeline. A user can see a glimpse of a note in a format similar to this (https://tinyurl.com/y3sswyaj). Instead of year, in that photo, it would a 'glimpse' a small viewports in which they can see the file theyre currently working on it's past, or current state. The client side app would focus on being visually appealing, as well as functional. When a user logs in theyre presented with a basic view where they can either create a new note, or navigate to their 'notebooks', from which to pick a note.  Mobile view would be smaller icons. instead of the timeline being on top, it would be on side, going down, and user has to 'drag' it onto the screen, like a menu.
Below their Navbar, for a specific note would be the timeline for the note, and all its past states would be there. Either the user can save a state, and 'branch off to a new state, in which they either COPY everything from the last state, and continue on it, or have a fresh page, depending on their needs. Backend would connect with a DB to store users, and data, maybe encrypt data?
I think this app would be useful for learning new things. 
If it's code, you can see how a library, or function develops over time and get a better understanding of whats going on(kind of what blogs are trying to do, but you scroll down forever, and often you only ever get snippits of the code, and have to navigate the page a lot).
If its math you can better understand the steps to solve an equation for eg
If its a histroy class you could make each 'glimpse' be a year for eg, and youll always ahve the visualy cues available as you could see the timeline, and remember the facts for that specific year more easily
) 

It would be an evernote & github on crack