12 Best Free Anti-Spam Plugin for WordPress

1. Akismet

2. SI Captcha Anti-Spam

3. Anti-spam

4. WP SpamShield Anti-Spam

5. Antispam Bee

6. Stop Spammers Spam Prevention

7. Advanced Invisible Anti-Spam

8. WordPress Zero Spam

9. Growmap Anti Spambot Plugin

10. NoSpamNX

11. WP Bruiser

12. Spam Destroyer

Source: https://codegeekz.com/wordpress-anti-spam-plugins/