I find a single pane outliner the best for me. You can nest, group and move ideas around quickly. For windows, the best still is Ecco Pro. It's a free software

I find a single pane outliner the best for me. You can nest, group and move ideas around quickly. For windows, the best still is Ecco Pro. It's a free software written back in the 90's that has an awesome outliner. I know there are many other windows based single pane outlines but I have not used windows for my desktop for several years. On Linux, which is my primary desktop, I use Ecco Pro on Wine. If using OSX / IOS, I would recommend Omni Outliner. Regarding two pane outliners vs singleness pane, I simply don't find the fragmentation of information across two panes intuitive. This may be subjective though. To me, having all information in a single tree, flows much better when brainstorming. For Android, I don't have many good options for Outlining and therefore a regular note taker for now that's Evernote.