Triq is a pure Erlang implementation of the QuickCheck style of testing.
Triq (pronounced "Trick Check") is a free alternative to QuviQ eqc. Triq's API is modelled closely after eqc, so I recommend their tutorials and slides for an introduction to QuickCheck. Notice that QuviQ eqc has many features not found in triq, but it is open source licensed under the Apache license. For instance, eqc has features for reporting, management, probably a much better shrinking mechanism, cool C integration, and professional support.