At work we have a home grown web based database app where we can log start and end times of a task. IT disallows overlapping registrations, and at most one task can be open (no closing time) at any time. So you stamp when you start, and stamp again when you stop, or start the next task.

It can do summaries per project or per type of task, or just total working times for any week.

The hassle is so low that it's not a problem to use it, as it only takes 10 to 15 seconds to complete a detailed entry, even for me, and I used to hate registering before this.