And like most ideas, an outline isn't confined to one location, such as your Mac. In 2011, The Omni Group extended the flexible outlining capabilities of its OmniOutliner Mac app to the iPad by releasing OmniOutliner for iPad ([four stars]). Now, with the release of the universal app OmniOutliner 2.3 for iOS (App Store link), you can work with your outlines as inspiration (or perspiration) strikes on the iPhone as well, no matter where you are.
Appearance is important
OmniOutliner got a major rehaul in version 2.0 to reflect the modern iOS 8/OS X Yosemite visual style, including cleaner lines and no more faux rounded buttons and toolbars. I hesitate bringing that up right away, since the appearance of an interface is usually one of those things you're supposed to notice and forget in favor of how the app's features actually work.
But as version 2.3 goes universal, the appearance is important because even the larger screens of the iPhone 6 and iPhone 6 Plus don't offer an expansive view of a sprawling outline. The minimal interface gets out of the way so you can focus on the outline, even on a relatively puny iPod touch (Figure 1). The text zoom defaults to 120 percent (you can adjust it manually if you like), which works well, especially if you're viewing the same file on multiple iOS devices.
It's also easier to see which items are selected when working in a complicated outline. This is a tiny detail, but when you select a parent row, a faint line appears to indicate which child items belong to it (Figure 2). The interface for selecting and acting on multiple rows is also cleaned up. In the original version, you'd tap the Edit button, which introduced a new set of round selection buttons at the right edge of a column. Now, when you tap that button, you use the existing row handles at left to make selections. From there you can cut, copy, delete, group, or move the rows as a group.
Version 2 also enables you to apply new template themes within a document if you want to change the overall appearance, as well as save any custom theme changes to new templates. (That's particularly helpful if you've tweaked the styles to suit your own projects and want to create new documents based on that appearance.)
How well it works as an outliner
OmniOutliner for iPad already included the bulk of the malleable features found in the desktop counterpart, and OmniOutliner 2.3 continues those with an extra dose of performance.
In documents with multiple columns, you can drag on the screen with one finger to reposition your view and expose columns that appear off the screen. As with the previous version, you can restrict the data types used in the columns, such as limiting a column's cells to just numbers or dates. (And I appreciate that the app is smart about its data, letting me type something vague like "Friday" into a cell and automatically converting that to the correct date.)
When scrolling down through long documents, the app still needs to occasionally pause and load more content (as it doesn't load the entire document into memory), but this feels faster and less obtrusive than in the original version.
Repositioning rows is a simple matter of drag and drop, with a visible guide that indicates exactly which outline level you're targeting.
As you're creating a new row of data, it's simple to indent or outdent the level using buttons at the lower-left corner of the work area--which just happens to be where your left thumb is positioned while thumb-typing on the iPhone's screen.
I did run into one anomaly: When adding new rows to the bottom of an outline, the cell is initially hidden behind the document's headers, but it pops into view when you begin typing. (I reported that to the developer.)
Not long ago a "mobile" version of an application didn't carry many expectations; it could get away with just viewing documents. Now, however, we expect not only editing but a way to make the documents appear wherever we are, with as little friction as possible. OmniOutliner takes full advantage of Omni Sync Server, a free service the company built from scratch when it became clear that iCloud wasn't going to work for them. You can also sync using your own WebDAV server, or add outlines to the Local Documents storage area via cumbersome iTunes sync or by transferring a file from another application using the iOS Open In mechanism.
In my experience, Omni Sync Server is the model of cloud syncing. When you update an outline on the iPhone, for example, the edits are reflected on the iPad and in OmniOutliner 4 for Mac within seconds, even when the document is open on all the devices simultaneously.
If a document is edited in two places before they're synced, the server displays two copies, with the source added to the title, such as: "Test Outline (conflict from mobile on iPhone 6)." Although I'd love to see a way to highlight differences between the documents, it's a nice touch that when you delete one version, the file name reverts back to the original and doesn't litter your documents list with messy conflict names.
Speaking of the Documents view, I would like to see an option to view documents as a text list instead of just the grid of previews. It can be difficult to parse long document titles when they run past the border of the document's box, especially on the iPhone. Also, editing a filename means tapping the title on this screen, which is a small target on the iPhone. Currently the only custom viewing option here is to sort the documents by date or title.
A newer, better outliner
The big news about OmniOutliner 2.3 for iOS is its ability to run on the iPhone as well as the iPad, but it's worth noting a few welcome features that were added in version 2.0. There are settings specific to using an external keyboard with the app: using the Tab key to navigate between cells, showing keyboard shortcuts in inspectors, and typing Command-V to paste text styled or plain. The app can import text shortcuts from TextExpander if it's installed. And additional templates from OmniOutliner 4 for Mac are available.
Like the ideas you'll be working on, OmniOutliner 2.3 for iOS is evolving nicely.