Searchcode — Searchcode: Search real-world examples of functions, APIs, and libraries in 243 languages across GitHub, GitLab, Bitbucket, GoogleCode, and other source code repositories.
Sourcegraph — A fast and functional search engine for open-source repositories, with a self-hosted version available. selfhosted.
HotExamples — Search for code examples of an open-source project, enabling the viewing of examples using a particular class or method from multiple projects on one page.
Libraries.io — Search 4,690,628 packages across 32 package managers.
RepoSearch — Search source code in SVN and GitHub repositories
grep.app — Git content, useful for locating strings associated with IOC vulnerabilities and malware.