A lightweight (~217 bytes vanila JS at frontend) and privacy-friendly plugin to prevent spam comment in the default commenting system of WordPress. Works instantly. No settings required. No captcha.
Akismet Alternatives
Akismet is described as 'Checks your comments and contact form submissions against our global database of spam to prevent your site from publishing malicious content' and is a Anti-Spam tool in the security & privacy category. There are more than 10 alternatives to Akismet for a variety of platforms, including Web-based, Wordpress, Self-Hosted, Linux and Mac apps. The best Akismet alternative is Antispam Bee, which is both free and Open Source. Other great apps like Akismet are StopForumSpam, YouTube Spammer Purge, Signal Spam and CleanTalk.