It's more than you ask for and has a significant learning curve, but Emacs' org-mode can handle that workflow. Just create a task, give it an effort estimate, clock it in, and when you reach the time you estimated, it raises a system notification.
In the agenda view, you can get it to output a clock-report in the form of a table for all the tasks you did in a given period of time. The columns are customizable with arbitrary expressions, so you can get it to tell you how well you did against your estimates in any form you want (percentage of estimate, 2 columns giving you both times, a time difference between the estimate and the time you took, etc.).
I'm using more or less the workflow outlined here:
In the agenda view, you can get it to output a clock-report in the form of a table for all the tasks you did in a given period of time. The columns are customizable with arbitrary expressions, so you can get it to tell you how well you did against your estimates in any form you want (percentage of estimate, 2 columns giving you both times, a time difference between the estimate and the time you took, etc.).
I'm using more or less the workflow outlined here:
http://doc.norang.ca/org-mode.html