mnoGoSearch - Open Source Search Engine

Indexing and search engines separate applications.
Supports a huge number of character sets, UTF8, Cyrillic, East Asian langauges, and has a character set guesser for 70 charset/language combinations.
Metadata tag indexing features
HTML templates for search results
Written in C
Also front-end interfaces in PHP, CGI and Perl
(Windows version is commercial)

Indexing and search engines separate applications.