Zebra is a high-performance, general-purpose structured text indexing and
retrieval engine. It reads structured records in a variety of input formats
(eg. email, XML, MARC) and allows access to them through exact boolean
search expressions and relevance-ranked free-text queries.

Zebra supports large databases (more than ten gigabytes of data, tens of
millions of records). It supports incremental, safe database updates on
live systems. You can access data stored in Zebra using a variety of Index
Data tools (eg. YAZ and PHP/YAZ) as well as commercial and freeware Z39.50
clients and toolkits.

Homepage:
https://www.indexdata.com/zebra
