Google Scholar - Google Scholar is a freely accessible web search engine that indexes the full text of scholarly...

EasyBib - Automatic works cited and bibliography formatting for MLA, APA and Chicago/Turabian citation styles.

Scinapse - Scinapse is a free, nonprofit, Academic search engine for papers, serviced by Pluto Network.

Paperpile - Clean and simple and reference management for the web. Sync your PDFs to Google Drive and cite your papers in Google Docs.

SemanticScholar - An academic search engine that utilizes artificial intelligence methods to provide highly relevant results and novel tools to filter them with ease.

Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.