This module provides a framework for easily creating searches on any entity known to Drupal, using any kind of search engine. The module on its own is pretty much useless and needs at least another module that defines an actual search backend (called "service class"). Its use lies primarily in enabling developers to easily create new service classes, while this module takes care of all generic tasks. It also enables site administrators to seperate the definition of indexed content from the search server it lies on, thus enabling almost complete backend-independence.
At the moment there is only one backend available, a simple database-based solution. Nevertheless, the module is even in this state more powerful than the Core search in some respects, foremost in flexibility and in being able to index any entity out-of-the-box, even ones defined in contrib.
The planned future development includes a Solr backend, a Views integration (for displaying search results with a view), facets and the implementation of some features still missing compared to Core search (e.g., highlighting). However, all of these can already be added with contributed modules, no modifications of the basic API will (probably) be necessary. This ensures that all those features can be used with any backend and any entity type.
Extensive documentation for other developers who might want to extend the framework's capabilities themselves is available. If you are trying to implement some extension point and are stuck, please don't hesitate to ask in the module's issue queue (or contact me directly).