Codex is a web application for setting programming exercises in a learning environment (e.g. programming classes).

• allows flexible Markdown "wiki"-style mix of documentation and exercises
• allows testing single units rather than complete programs (e.g. functions)
• it can provide automatic feedback (failed test cases)
• supports Python (using doctests), and Haskell (using QuickCheck); C is also suported using the Haskell FFI

The user guide is available here.