Toggl Time Tracker other than the free Android app has a web app as well as a desktop app that are free and sync time recorded in each to the cloud, so no matter what device and app that is being used, they are all up to date on the days activities.
Graphical timesheets placed in the calendar allows for an easy visual representation of how much time was used on what tasks on what hours for what days.
There is a free version available with limited functionality that is great for freelancers as well as testing the app. There is also a 30 day free trial for the paid versions for further testing.
TimeCamp can create an invoice based on your project hours. The app will take care of the math for you, you just need to provide it with the rate and tax. TimeCamp can also export directly to Xero or Quickbooks.
Time Recording has built in Android Wear integration, allowing for even easier check in and check outs by using the watch instead of pulling out the main device.
Everything is safely backed up to the cloud. Lost your phone? No problem, download the app, login with your credentials and continue working with all of your data.