Krugle - Krugle is the complete enterprise solution for search targeted to the development organization.
Reactive Search - UI components for building Amazon / Yelp like Search
OpenGrok - OpenGrok is a fast and usable source code search and cross reference engine.
Searchkit - UI components for Elasticsearch
Sourcegraph - Sourcegraph is a free, self-hosted code search and intelligence server that helps developers find, review, understand, and debug code. Use it with any Git code host for teams from 1 to 10,000+.
Searchbase - Build Search UIs with drag and drop