Word collections cost nothing, and you can add to them wherever you are.

The Online Language Learning Database

Reduplicatives (willy-nilly)
Homographs
Mispelled Words
Three-Word Words (nevertheless)
Many ways to say one thing
Subs for long words
Self Description
Adjectives for only one noun
Neologisms
Make [Adjective] (make purple = empurple)
Queries
Invertable words 1
Invertable words 2
-less without -ful (feckless vs. feckful)
Frequent Words
Begin with "A" but don't end with "a"
Story with no "e"
Origin of "Goody two-shoes"
Clichés to avoid like the plague
Janus Words
Who makes the rules for English?

Lengthening words
Tenseless Verbs
Confused Studies (cosmology vs. cosmetology)
A guide to Midwestern expressions
Name Collections
Word Puzzles
Merriam-Webster word puzzles
Longest Palindromes
Anagrams
An Anagram Poem
Opposite Proverbs
Good words starting with "eu"
Similes (right as rain)
95% Metaphors
Where, whither, whence?
Animals as Verbs
Unusual Words
Expressions of Nautical Origin
Related Pairs (pathetic apathy)
Cockney Rhyming Slang
Misquotes
Why do I feel a 'but' coming?
Word-Hyphenation
"You're welcome."