FileProInfo - It's All About Files, Software, Online Tools - 100% Free
PreFlight - Preflight is an Automated Web Testing tool. Allows everyone to automate Web UI tests.
File-Extensions.org - Large computer file extension library with detailed explanation of each file type with links to download free or associated software programs.
Videogram - Auto create interactive thumbnails (GIF card) of video
FileInfo.com - FileInfo is the central file extensions registry and contains a database of over 10,000 file types.
Thumbnail Test - A/B Test Your Thumbnails & Titles Live On YouTube