Super Search can be downloaded freely (without support) on GitHub here: https://github.com/Solspace/Super-Search
Super Search greatly improves search functionality, allowing for powerful and flexible searching on channel entries in ExpressionEngine. It can be used both as a search engine and as a replacement for the Channel:Entries tag.
The architecture of the add-on borrows from Google's model of constructing search queries. Anything you might want to search for... keywords, channels, categories, statuses, authors, custom fields, date ranges, custom field numeric ranges, etc, can be loaded into a single URI segment with the Super Search syntax. This makes pages highly shareable, flexible and versatile. Searches can be performed in a variety and/or combination of a few different ways:
Super Search supports relevance-based searching, which allows you to create simple or advanced algorithms to control ranking of entries in search results. This is done by using the relevance-related parameters in the Super_Search:Results tag.
Super Search also supports Fuzzy Searching, which basically means that searches can be set to ignore plurals, match up similar words, and suggest other words based on spelling in search terms.
And finally, Super Search includes a Search Curation feature, which is designed to allow manual selection of entry results for keyword searches. This would typically be used as supplimental search results to normal search results, similar to how Google displays sponsored results at the top or side of search results pages.