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AbbreviationZ

Abbreviations by category and alphabetical order.
Acronym Finder

Comprehensive database of acronyms, abbreviations, and initialisms.
Filename Extensions

The three letters after the dot in a computer file's name (such the ".doc" in "resume.doc") are called the extension and they tell you what kind of file it is. Here's a comprehensive listing of those extensions.
Internet Anagram Server

Input a word and get all possible anagrams.