Redirector: Extension for Firefox and Chromium that can manually be configured to process Inidious Redirects. For details, see the setup page to use it with Invidious.
Userscripts for Invidious.
Invidious Redirect: Redirects YouTube URLs to a deprecated instance, but can be edited to redirect to a different instance.
YouTube to Invidious: Scans current page for YouTube embeds and replace with invidio.us. (Can be edited to use any preffered instance)
No-Youtube: Userscript to replace youtube links to invidio.us. Can be edited to redirect to a preffered instance.
FYTE: Replace all YouTube embeds on a page with the video's thumbnail. Click on the thumbnail to play the video. Invidious is supported in the Options panel (redirects to invidio.us by default, can be edited).
Privacy Redirector: Userscript to automatically redirect to different private frontents, including Invidious. Can be configured to redirect to specific instances of the user's choice.
Simple Sponsor Skipper: Userscript based on Sponsorblock that is pre-configured to work with multiple Invidious instances, but can be easily altered to use any instance desired by the user.
Invidious Preferences Userscript Userscript for enforcing preferences accross multiple instances, through URL Parameters, and without using browser cookies. Works in tandum with Privacy Redirector and Simple Sponsor Skipper. See here for more information about URL Parameters.
Extensions that integrate Invidious into other programs and apps
UntrackMe: Android app to rewrite YouTube links to Invidious. Can optionally play videos in the app as well.