Free Online Tools

Editor

draw.io - draw.io is free online diagram software for making flow charts, process diagrams, org charts, UML, ER and network diagrams.
Cloudcraft - Draw AWS diagrams with Cloudcraft.

Epoch & Unix Timestamp Converstion Tools
Unicode Converter - Decimal, Hexadecimal Character Codes in HTML Unicode
Free online file conversion - Zamzar supports over 1200 different conversions.
Online PNG and JPEG compression - Compress your PNG/JPG files by up to 80% and retain full transparency. (Recommended by Amelia)
Enjoy Encoding and Decoding - DenCode supports various encoding/decoding algorithms.

IPv4 Subnet Calculator - The IPv4 Subnet Calculator performs subnet calculations for the given network address block, subnet mask, maximum required hosts per subnet and determines the resulting broadcast address, subnet, Cisco wildcard mask and host range.

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FreeDNS - Free DNS Hosting, Dynamic DNS Hosting, Static DNS Hosting, subdomain and domain hosting.

SSL Server Test - This free online service performs a deep analysis of the configuration of any SSL web server on the public Internet.
Observatory by Mozilla - Observatory by Mozilla is a project designed to help developers, system administrators, and security professionals configure their sites safely and securely.
SSL Certificate Tools - You will be able to troubleshoot, test, check, generate, verify, convert, and otherwise manage many common SSL issues using simple SSL Tools.
SSL For Free - Free SSL Certificates in Minutes
StartSSL - StartCom charge the identity validation fee only, all certificates are FREE and unlimited.

Browser Compatibility Test - Browsershots makes screenshots of your web design in different operating systems and browsers.
PageSpeed Insights - Make your web pages fast on all devices.
Mobile-Friendly Test