For a long time, syncing files was a huge pain. It involved portable disks of one sort or another and lots of walking and fiddling. Then a few years ago cloud syncing services showed up and Dropbox quickly became the solution to most of our syncing problems.
Then Apple jumped in with iCloud and the idea that documents could just sync across multiple devices without opening the Finder and endlessly pressing "Sync" buttons.
Around the time that iCloud first showed up, I spoke with Ken Case, president of the Omni Group, about syncing between the Omni Group apps on my iPad and the Mac. The Omni Group did not jump on the Dropbox or iCloud bandwagons. As Ken explained it to me, the Omni Group prides itself on providing the best experience to their customers and if they were going to start syncing data between their apps, they didn't want to rely on anyone else. Specifically, they didn't want to be on the phone with a customer only to say, "Sorry. The app is working right. Your syncing problem is Dropbox or Apple." The Omni Group wants to own your experience with their apps soup to nuts. Now they do.
The Omni Group built its own sync engine. It's called OmniPresence and it is great.
On the Mac, OmniPresence installs to your menubar. When you first set it up, it adds a folder to your Mac, just like Dropbox. (Though don't locate your OmniPresence folder in your Dropbox folder. That's like crossing the streams.) You can drop any OmniOutliner, OmniGraffle, or OmniGraph Sketcher file in that folder and it immediately gets synced up to the cloud. The icon animates with three dots when there is network activity and clicking on it gets you quickly to your OmniPresence folder.
Then when you install the app on your other Macs, those same files get synced to your magic OmniPresence folder. Because this is just another folder on your Mac, the OS X Versions and Auto Save features just work.
The Omni Group has also built in OmniPresence syncing to the current builds of the OmniOutliner, OmniGraffle, and OmniGraph Sketcher iPad apps. Those apps also see the files in your OmniPresence folder.
Using OmniPresence you can have a file open on your Mac and iPad at the same time and changes made on one platform automatically populate over to this other platform. This part is just like iCloud.
They even made a clever video.
That's the thing about OmniPresence. It's Dropbox and iCloud all rolled up into one. And then when you have a problem you can call Omni and they control all the pipes to make it right.
The Omni Group also has a more extensive tutorial that is worth the three minutes it takes to watch.
The whole thing is baked right into the Omni Group's Omni Sync service. That's how I use it. However, if you want to install it on your own server and keep your data private, you can. OmniPresence works with any properly configured Apache server, which means you can host your own data without having to install any special software from Omni. It even works on HIPPA-compliant services like SwissDisk. The Omni Group has also open sourced the syncing code for iOS apps at github so expect other app developers to start using it too.
Ken Case explains this best. "OmniPresence is not yet another proprietary syncing solution just for syncing Omni apps. On the Mac, it's designed to work with documents from any other OS X app that supports Auto Save and Versions--such as OmniGraffle, OmniOutliner, OmniGraphSketcher, or even Apple's built-in TextEdit app."
There are many nice little touches to OmniPresence. For instance, you can sync multiple folders to different accounts so you can keep your work and personal documents separately.
While OmniPresence is just at version 1.0, I think this is going to become a big deal. It offers a legitimate third options to users and developers to sync data between devices. Its combination of syncing in real time without having to press "Sync" buttons and simple folder accessibility on the Mac make it compelling.
You can learn more from the OmniGroup. If you already have an Omni Sync Service account (you should), I encourage you to log in and enable OmniPresence and check it out for yourself.