My favorite apps (mostly games ) I use on my Zio are:
1. Texas holdem live
*allows chat, tournaments, low or high bid tables, and daily log in bonus...occasionally force close but not often... and chat filter sucks a bit.. it overall a fun game/app.
2. Vampires live
*much like all the other mission based games but I have a lot of friends here.
3. Palringo
*awesome app for chatting with friends or making new friends
4. Words with friends and Word feud
* both are similar Scrabble base games

All these apps are free