I'm looking for a task time tracking app (android, and/or desktop Linux)

I'm trying to keep a log of the time that I spend doing specific tasks throughout the day. Currently, the way that I am doing this is by constantly running a stopwatch and filling out a spreadsheet for the day — when a task is completed, I lap the stopwatch and add the task and the time spent on that task in a row in the spreadsheet. It does the job, but it is very tedious. Does anyone have a recommendation for an app that can do this for me? I would like it to:

• Log the time constantly (when a task is completed, immedately start a new task)
• Time a task
• Allow naming of tasks
• (optional) Allow categorizing of tasks with tags
• (optional) Show graphics for how time is spent each day, and statistics on how much time is spent
• The ability to export the data (e.g. CSV)

It would probably be the most convenient for this to be an Android app, but I am also open to suggestions for a Desktop (Linux) app.