Anti-Spam Test: Introduction

I have been thinking recently about porting Drupal's 'Antibot' module to Backdrop CMS. On the five Backdrop sites I've built to date I use the 'reCAPTCHA' module, however I'd like to get away from needing a separate (Google) account to avoid spam, and requiring users to take an extra step to submit a form (tick a checkbox to prove they're not a robot). Antibot looks good in this case, as it...