Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Diigo - Diigo is a powerful research tool and a knowledge-sharing community
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Weava - Workspace to highlight, organize & collaborate on your research articles.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.