Zettair is a compact text search engine for indexing and search of HTML (or TREC) collections. It is an open source software developed by a group of researchers at RMIT University.
Its primary feature is the ability to handle large document collections (100 GB and more). It has a single executable, which performs both on-the-fly indexing and searching, with a command-line interface.
It is licensed under the terms of the GPL license.
References
Zettair Wikipedia(Text) CC BY-SA