ITmaze is a consulting company that needs to invoice its clients for time spent on projects. Tracking time can be a complicated experience, but two Android apps make this a whole lot simpler: rtime-rec and CallTrack. Both apps log to Google Calendar. I use a separate billing calendar, just to log client activity.

rtime-rec
by rmiya

Logging projects to a Google Calendar is simple. You launch the app, tap on the day, choose a title (I use my client's name) and tap now. When you're done, go back in, tap on the now button for the end time, add a note and it's logged.

CallTrack
by asterdroid mobile

Logging incoming and outgoing calls will add a whole new dimension to your client logging data. Once activated, this app just does it's thing and logs to your selected calendar.

Finally, I use a few little scripts to export my billing calendar to ics, then to csv and then into my accounting software.

Tip for new players: Calendar activities can overlap, so don't bill your client for the phone-call you made while you were working on their project :)