Timing-and-estimation-plugin is a project mainly written in PYTHON and JAVASCRIPT, it's free.
Git mirror of the Trac hack TimingAndEstimation plugin, plus the stopwatch widget for the "hours" field.
The TaE maintainer, Russ, has been very positive about this widget and has already integrated the plugin upstream.
Although this has already been integrated upstream, I may have some changes here from time to time. I try to pull in the upstream TaE changes to ensure the plugin integrates cleanly.
The 'master' branch has a ready-for-install replacement of TaE 0.11.