Workflowy, CherryTree, Dynalist, EssentialPIM, Story Planner for Writers, Plottr, Manuskript, Org mode, Storyline Creator, Tkoutline, CrossLine, Foldout, Walling, MyLifeOrganized, Ecco Pro, Orgzly, Opal, Listography, TreeLine, wikidPad, MyInfo, True Novelist, Perpetual Notes, Orgzly Revived, Notea, Writing Outliner, CarbonFin Outliner, buzz.opml, MemPad, Cloud Outliner, Outspline, Yarny, Cloud Outliner Pro, BucketListly, The Outliner of Giants, Vimflowy, Fargo, Deep Notes, ProCite, Qbase, BlankPage.io, LeafNote are some alternatives to OmniOutliner.