Orgzly - Outliner for notes, tasks and to-dos
Workflowy - A better way to organize your mind.
MemPad - MemPad is a plain text outliner and note taking program with a structured index.
Swift To-Do List - Swift To-Do List is software that helps the user stay organized with advanced planning and lists. The software is developed by Dextronet, a Prague based company which was founded in 2004 by Jiri Novotny... read more.
OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.
OutlineEdit - A beautifully crafted outliner for your Mac: