Solr has a great way to plug in components, which they call SearchComponents into a request. This enables different components to be chained together to add new functionality without writing any code. Once a component is created, integrators can plug that component to be used in their applications (web or otherwise).

Solr has a set of default SearchComponent like MoreLikeThisComponent, HighlightComponent, etc and this month, another has been added to the list - SpellCheckComponent. This was in works for sometime, but now is out to be used.