This is a miscellaneous collection of tools you may find useful. I use them from time to time, and make them available for others to use here. I may add/remove/change them at any point.
Browser - Show the information your browser transmits. Useful to check the headers your browser transmits on every page load.
HTTP - You can simulate a slow HTTP load using a link to this page, or simulate a HTTP error messsage like 404. Useful for testing how a script treats a slow/error URL.
QR Code - Just a simple QR Code generator.
Sync - Lets you generate a URL, and you can add some text or upload a file. You can generate a QR code to open the same link on another device (phone/tablet). You can upload and download files from any device. I use this to quickly get a file to/from my phone when I'm on a computer other than my own.
TCP - Quickly test a TCP port to see if it is open, closed, or stealthed.
Textify - Quick browser based text replacement. I usually use this for multiline Find and Replace.
URL - Check a URL to see the response and headers sent. Redirects are not followed, so you can see what a link shortening device returns eithout visiting the final link. Allows you to see Certificates sent by the server as well.
WHOIS - Simple domain WHOIS checking. Works for common suffixs (like .com), but may not work for some newer suffixs.