Uncaptchalous is a project mainly written in JavaScript, it's free.
Drupal 7: Unobtrusive form spam filter
Unobtrusive form spam filter. Unlike a captcha it requires no human/computer interaction. Unlike akismet, it does not rely on a third party service. Theoretically, a bot could be purpose built to defeat it - but it should provide protection against general purpose spam-bots.
Enable the module. All forms will be protected.
6.x-1.0-beta3 Implemented form visibility settings
6.x-1.0-beta2 Changed package in .info from Levelten to Spam Changed javascript to use Drupal.behaviors instead of $(document).ready() to work with dynamically generated forms
6.x-1.0-beta1 Initial Release
Developed by Dustin Currie [email protected].