This is an absurdly simple timecard program. The entries are all kept in
a single text file. Each "slot" is delimited by a blank line, and
contains a start time, an end time, and some comments. If the slot is
still "open", then the end time is listed as "INPROGRESS".

You can use it like this:

  timecard in 'working on foo'
  timecard out
  timecard edit ;# manually munge the data
  timecard sum ;# total hours worked
  timecard list ;# per-slot report

The data is kept in the ~/.timecard file. You can override it with the
$TIMECARD environment variable.

There is also a wrapper script "clock" which keeps a timecard in a git
repository. It pulls before running timecard, and commits and pushes
afterwards, which gives an approximation of a centralized system. You
must have ~/.timecard already set up as a git repository.

Note that there is no support for marking entries as "invoiced" or
anything like that. But you can do it manually like:

  clock sum | mail -s 'pay me'
  cd ~/.timecard
  git mv timecard invoiced/2009-11-01
  git commit -m 'november invoice'