Git Paid is a console time tracking program that stores work logs in Git. Currently, it assumes begin and end commits are accurate in time and uses this to generate an invoice. In the future, user-supplied billable hours will be supported.
See gpbegin(1), gpend(1), and gpinvoice(1) for more details if this example isn't enough for you.
$ gpbegin -b client-name
$ ...
$ gpend -b client-name -m "Shaved the yak."
$ gpbegin -b client-name
$ gpend -b client-name -t 1:45 -m "Faked the time."
$ gpinvoice -b client-name
# Invoice
Thu Jan 6 18:27:32 UTC 2011
from client-name branch of /home/vagrant/.gitpaid
## Work log
Began: Thu, 6 Jan 2011 16:17:29 +0000
> Shaved the yak.
Ended: Thu, 6 Jan 2011 17:47:42 +0000
Billed time: 1:30
Began: Thu, 6 Jan 2011 18:27:23 +0000
> Faked the time.
Ended: Thu, 6 Jan 2011 18:27:25 +0000
Billed time (adjusted): 1:45
## Summary
Total billed time: 3:15