Facebook Messenger - Facebook Messenger is a faster way to message.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.