It seems to me this could be a smartphone app. Whenever a person wants to make a prediction about a personal event, they click on the app and speak, with a pause between the thing and how likely you think it is. The app could just store verbatim text, separating question/answer, and timestamping recordings in case you want to update your prediction later. If you learn to specify when you think the outcome will occur, it can make a sound to remind you to check off whether it happened; otherwise it could remind you periodically, like at the end of every day. Why couldn't it have data analysis tools to let you visualize calibration, or find useful patterns and alert you? Seems a plausible app to me.