Freeplane - Freeplane is a powerful and free software for building mind maps.
Adobe Acrobat DC - Make your job easier with Adobe Acrobat DC, the trusted PDF creator. Use Acrobat to convert, edit and sign PDF files at your desk or on the go.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Wondershare PDFelement - All-in-one PDF editor
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.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.