Last week it was announced that that real-time collaboration is being added in all iWork apps: Pages, Numbers, and Keynote. Apple has updated its iOS versions of the apps, accordingly.
Pages is a word processing document; Numbers is a spreadsheet app; and Keynote is a presentation creation app. All three apps cost $10 each, but are included with new iOS devices. All three are available for both OS X (at the Mac App Store) and iOS (at the Apple App Store) devices.