Patryk

Redirect any “not found” (404) page to homepage with 301 (SEO) redirect code + Google Analytics (utm_source=404&utm_medium=Redirect&utm_campaign=404)

PRyC WP: 404 to Homepage 301 redirect

Redirect any "not found" (404) page to homepage with 301 (SEO) redirect code + Google Analytics (utm_source=404&utm_medium=Redirect&utm_campaign=404)

brainfruit

This simple plugin – which is also WordPress network compatible – automatically redirects 404 errors to the best matching and existing content in your WordPress blog. 
The matching is based on the slug of the content not found and searches also on taxonomy pages (tags & categories). This is perfect when you have changed the permalink settings of your taxonomies. 
All redirects are permanent (301) which is a SEO best practice. 
Since this plugin doesn’t need any configuration it works perfect in WordPress Network / multisite setup.

404 ReDirector

Simple, SEO friendly, permanent (301) and automatic redirect of 404 errors.

PRyC WP: 404 to Homepage 301 redirect vs 404 ReDirector