I installed ManicTime last week and have thus far found it to be excellent. It doesn't pop-up and remind you to fill it in, but it is very easy, at the end of the day, or whenever, to open it and assign tasks based on the Applications or Browsing timelines. It does remember the tasks you previously entered and it is easy to call them up again, and yes, you can right-click to assign a task. I suggested, but the author already has in mind, some kind of task list editor. The biggest concern I have is that it will force me to be more careful with distractions like browsing - there is no ignoring what you have / have not done with this thing - it's all there in
black and white colour!
You should at least check out the demo videos on the website and install it if you think it may help. I have used a couple of home-scripted (AHK) Time-loggers in the past but I suspect this beats anything I could produce myself. If I do find myself ignoring it when the novelty wears off (hasn't done yet) then I may write a script to pop up MT once an hour. Or make a suggestion to the very receptive author.
It has an excellent Tag export to CSV function which can provided a report of Activities for any period, which can be opened in Excel and is in a format which allows Excel to sum any Activities.
Slight concerns include: memory usage - currently sitting at 55Mb in Task Manager so not a lightweight; and data storage. After a week, there are two data logs of 2Mb and 3Mb each, so after a year it could be quite hefty. I may suggest to the author that it would be useful to be able to clear out or thin the Application data for past date ranges, when far enough in the past that you have tagged your Activities, but no longer need to know what applications you were using every minute of the day.
Nonetheless a great piece of software and deserves your attention if you have a requirement to log time by reference to PC-based activities. I have a strong feeling I'll be sticking with this one.