Find anagrams of words and "words that can be made with a set of letters" (sort of a sub anagram)
Automatic migrations for Ecto as part of the application boot process
Priority Queue for Elixir. Heap implementation
Sudoku solver in Elixir, which prefers to use heuristics over guessing
XML-RPC encoder/decder for Elixir. Supports all valid datatypes. Input (ie untrusted) is parsed with erlsom against an xml-schema for security.