One thing to keep in mind is that, on Mobile9 DECO, a lot of the applications and games that you can download aren't necessarily reliable. For example, you'll find modified versions of very popular games, but though they seem appealing, it's probably better not to risk it.
In the rest of the categories, you'll find safer content to download. The video tab, for example, lets you download videos from YouTube. In the book tab, on the other hand, you'll find all kinds of audio books, ebooks, and manga. And in the ringtone tab, you can find music by artist or the name of the song.
Mobile9 DECO is a very comprehensive application, thanks to which you can download practically anything: books, apps, music, videos, etc.