BeeCanvas is an online whiteboard based visual collaboration tool.

CherryTree is an hierarchical note taking application, featuring rich text and syntax highlighting, storing data in a single xml or sqlite file.

Evernote is a note taking application which keeps the notes taken in sync across all platforms using its cloud infrastructure.

Joplin is an open-source free note taking and to-do application.

Mendeley is a free reference manager and an academic social network.

Notezilla is a sticky notes app for Windows.

lumio is an online content organizing platform.

Diigo is a powerful research tool and a knowledge-sharing community.

footnote is a very light and neat Notebook App for elementary OS.

Leanote is a self-hosted note taking app.

NixNote is an open source client for Evernote.

ResophNotes is a fast note writing tool and a Simplenote client on Windows.