Lush is no longer free. $2 to d/l the app.
Highball, free but requires the latest iPhone update to use is another handy and shareable cocktail app.
While I havent found any cocktail apps are going to replace a great mixologist anytime soon 
having a handy pocket guide for the most common mixed drinks very handy. Say, I am at the liquor store and the employee is about as clueless as I am, I pull out my phone, open the app and purchase the right liquor option in the quantity I will need (party or drinks for two). That alone makes the app a tool.
I haven’t used any of the apps that cost $5 or more because if I want alot more detail I will go to the library or read up online.
