Our application (C#/.NET) needs a lot of queries to search. Google’s 50,000 policy per day is not enough. We need something that would crawl Internet websites by specific rules we set (for ex. country domains) and gather URLs, Texts, keywords, name of websites and create our own internal catalogue so we wouldn’t be limited to any massive external search engine like Google or Yahoo.
Is there any free open source solution we could use to install it on our server?
No point in re-inventing the wheel.
DataparkSearch might be the one you need. Or review this list of other Open Source Search Engines.