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.
Freeplane - Freeplane is a powerful and free software for building mind maps.
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.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
SuperNotecard - Introducing SuperNotecard. SuperNotecard is an online writing tool that features virtual notecards to help arrange facts or scenes, track details, organize paragraphs, and clarify your composition process.