Ecco Pro - Ecco Pro was a personal information manager software based on an outliner.
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.
InfoQube - Full-featured Information manager, inspired by award-winning Ecco Pro.
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.
OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.