SWISH-E - Open Source Search Engine

Written in C with a lot of Perl for customization, code library with API, for Unix and Windows
Local files or robot spidering
API for adding new index gathering options
Boolean and various fuzzy queries
Index and search meta tags and XML
Sort results by relevance, date, size, other fields
Special cases for special words with punctuation
Merge results from multiple indexes

Written in C with a lot of Perl for customization, code library with API, for Unix and Windows