For retrieval it uses Don Metzler's Searching using Markov Random Fields (SMRF) Java implementation. You can read his publications on the topic. It's exciting to finally get a chance to play with the implementation of one of the state-of-the-art retrieval tools. To my knowledge this is the first time Don's Java MRF toolkit for retrieval is available to the public.
Ivory is aimed at IR researchers as a platform for experimentation. This is an early release with a lot of rough edges.
Jimmy is using Ivory to index the ClueWeb09 dataset, which has 500 million English documents for the TREC web track.