If you're a Microsoft Office user, there's a little-known feature in Outlook you should know about. Outlook Journal can keep a detailed record of what you do during the day with little to no effort at all.
Journal is disabled, by default, and to get to this feature in Outlook, you have to click on the tiny drop arrow in the left navigation pane, go to "Add or Remove Buttons..." and select Journal. So it's no wonder few people use this feature.
It can, however, be really useful for time management and project tracking. You can set it to automatically log all task requests, emails, and meeting requests--from specific contacts or all of them. If you enable tracking on Office documents, you'll get a log of every time you work on Word, Excel, and/or PowerPoint documents--with the times and names of the docs.
You can view the log in a timeline or as an event listing. I used this to track my hours on projects for my timesheets, and it's a really easy, built-in tool helpful for remembering the details of everything you work on.
Adding journal entries is easy too, with a timer so you can record how long you work on something, and features like categorizing the entry, making it private, or linking it with people in your address book.
The "Share" option means you can easily send progress reports to your boss for accountability.
So instead of downloading a standalone time tracking app, give the built-in one in Outlook a whirl. [hat tip Make Use Of]