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+.
GitHub - Originally founded as a project to simplify sharing code, GitHub has grown into an application used by over a million people to store over two million code repositories, making GitHub the largest code host in the world.
OpenGrok - OpenGrok is a fast and usable source code search and cross reference engine.
GitLab - Create, review and deploy code together with GitLab open source git repo management software | GitLab
GrepCode - GrepCode.com is a code search engine built by developers for developers to search and browse open...
NotABug.org - Free open-source code hosting.