Please add a feature to allow the user to undo the last operation they did. Actually, multiple levels of undo would be even better.
A common use case is:
I'm working on a project and Klok is recording the time spent. Someone walks into my office and interrupts me or the phone rings, etc. It doesn't occur to me at the time of the interruption to change my "Working on" task in Klok. After the interruption ends, I want to edit the time entry for the task I was working on to reflect the fact that I really stopped working on it 15 minutes ago when a colleague came into my office for a chat. I'm also going to want to add a task to record that I spent the last 15 minutes in a meeting with my colleague. Often, in the process of editing the first task's end time and adding a new task, I'll make some sort of error and inadvertently click and drag a task when what I meant to do was select it so I could edit the start/end times, or I accidentally add an extraneous task that I didn't mean to add, etc. It would be very nice when that sort of thing happens to just be able to hit Ctrl+Z to take a step backward.