So, Apple is now testing iWork (Pages, Numbers, and Keynote) as a cloud service and place them on iCloud.com (their cloud service along with other apps that are available on most of their iDevices, such as Notes, Reminder, Calendar, Contact, etc). This means, you don't really need to install separate iWork applications (worth US$ 9.99 each) from App Store and just use Chrome or Safari to access icloud.com and have them available on your iDevice.
It's still in Beta phase and we are not sure whether it will be free or not, but for this beta, it's free for use. For best experience, it's recommended to use Safari, since when i used the latest Firefox on Linux, it showed a message that my browser is not fully supported when trying the Keynote. I couldn't see the slideshow when i click on the Play button as well. I guess only Pages works well with Firefox currently.
Taken from Apple's Knowledge Base:
The following browsers are supported for use with iWork for iCloud beta:
- Safari 6.0.3 or later (OS X)
- Internet Explorer 9.0.8 or later (Windows)
- Google Chrome 27.0.1 or later
- Safari 5.0 - 6.0.2 (OS X)
- Firefox 9.0 and later
- Google Chrome 7.0 - 26.0.1
Here's the screenshot of the main page of iCloud after logging in: