It looks like the developers, Workmates, have moved on and no longer support the app. Here is the TileDeck FaceBook page. Their last post there was in late 2011. There are two posts from early this year asking about that app, because it was no longer in the App Store.
I searched for Workmates in the App Store and discovered two app by them. One is similar to the TileDeck app, except instead of drawing the pattern your capture images through the camera and turn those into patterns. It also seems to be missing the professional features that allowed TileDeck to export the pattern for use elsewhere.
I'm sure there is similar software out there, but a quick search turned up nothing quite the same. The closest was PatternPanda, which seems to have some nice patterns, but they are mostly about selling some customized products.
I do have an app called SketchClub. It's a general drawing app tied to a forum/community, but some of the tools and filters are well suited to making patterns. It takes a considerably larger investment in time to learn but is probably more flexible in in the end. Other drawing apps may have the same or better features, but SketchClub is the only one I own that does patterns well.
Here is a quick example that took me about two minutes to create. It required a little drawing (mirrored both vertically and horizontal) a couple of filters; Offset which moves the inside to the outside to make a repeating pattern. Draw a bit more in the center (to fill in the now empty center) and transform to repeat the tiles as often as desired.
It can be exported in jpg, png, png with a transparent background, and psd (with all layers).
If you let us know what you need the app for it would probably help with recommendations; since TileDeck looks to be unavailable.