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.
Random Text - Generate random text which can be used for passwords. You can also generate random text from your own alphabet. No logs are kept of the text generated, and javascript is ran in your browser to randomize the results again before it is displayed.
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.