Metaculus has the capability to create private questions that only you can see
I use PredictionBook, which is not obviously better than a spreadsheet if you've already done the initial setup, but which did most of the things I wanted it to.
In the LessWrong dojo we did forcasts over the years in different ways.
On mode that was working decently was people setting goals to be achieved next week and stating their likelihood that they achieve the goals. People could bet against each other and we used a previously on LW published formula for calculating who should get how much as the bet resolves.
SquirrelInHell (who isn't alive anymore) wrote an Android App to track personal predictions (https://squirrelinhell.blogspot.com/2017/01/prediction-calibration-doing-it-right.html).
I don't think the skill is generally neglected. It's just that the efforts to train it didn't produce big utility.
I'm interested in personal forecasting - predicting my own future behavior on a range of timescales. I see it as a more useful skill than forecasting on world events. Formulating personally useful forecasts seems like an important and neglected skill in the rationalist community. And it would be nice to have some company, and tools to make it more convenient. Right now, I'm just using a spreadsheet. Does anybody know if there are groups doing this sort of thing? Is there a good app to manage the process?