These are third-party gadgets not created or hosted by me.
awesome-selfhosted – An awesome list of free software you can self-host on your own server.
coveryourtracks.eff.org – See how trackers view your browser
urlscan.io – Scan a website before visiting; shows a screenshot of the page
whynopadlock.com – Check SSL/TLS security of a website
securitytrails.com – DNS history; requires a free account
https://strudel.cc – Strudel; write dynamic music pieces in the browser