When I was trying to finish a college class in a week, I went to a remote office with nobody around, turned airplane mode on my phone, and created the following system.
First plan your to-dos for the day. Each to-do was something like "read chapter 2-3" or "take unit 5 quiz". I'd click on each one in my todo software and then write a log to give myself a feedback loop.
At the beginning of a session I would say what I wanted to accomplish and in what amount of time: "I want to read chapter 1 in 45 minutes". I'd then start a timer and race against the clock to try and get just that one thing done in that one period of time.
After the timer went off, I'd log what I did and how long it took me. e.g. "I got through chapter 2 and the first 3 pages of chapter 3. Great progress!!! I can do this!"
This gave me a return-and-report loop that kept me laser focused on the task at hand, with constraints, without losing perspective about the end goal.
One of the key insights here is that mini goals, small cycle times, and the loop leads to a snowballing effect of getting addicted to the focus and achievement that this system creates.
This app seeks to limit the tools and distractions needed to make this system work. I hope you find it useful.