Toggl is an online service and app that can help keeping track on what you spent your time on. For my purposes, to keep track of what I work on project-wise, I installed the Windows desktop which is shown in they Windows tray as a on/off icon.
The app supports nagging reminders if I have forgotten to enable tracking, and it supports the notation of Projects and Descriptions. The first means that it is possible to create multiple projects, such as the names of the projects that I am working on in the moment. The latter means that one can describe exactly what is being worked on in a specific project, e.g. “implementing rendering”, “testing rendering”.
This is a very powerful way of getting a quick overview of how time is spent across a project - if one remembers to track that is. On toggl.com, it is possible to see reports and dashboards of how time is spent each day or week.
It also support clients, i.e. who should be billed for the time spent, and team support, i.e. sharing time management between more than yourself and billing support. I have not tried to use these features yet, I am not even sure they are supported in the free version.
An advanced feature that the desktop application supports is auto-tracking. I have no idea how this feature works, but I believe it detects what I am doing and automatically tracks this on to one or more projects.