Android: If you're an at-home bartender and like to experiment with different drinks, Bartender for Android is the go-to app to learn how to mix just about anything, including a number of drinks you probably didn't know existed. The app's database is entirely crowdsourced, and full of both well-known and niche cocktails.
Bartender is a simple, free app that drops you to a massive list of drinks you can scroll through to find something you're interested in making. Tap the search button to look for a specific drink, search by ingredient, or filter based on drink rating to find the best drink recipes in the app to try. If you have a drink you love to make that isn't in the database, you can submit it from your phone. The sheer number of drinks Bartender can teach you to prepare makes it worth a download.
At the same time, Bartender's database is subject to all of the pros and cons that come with being crowdsourced. Some of the drink recipes are flat-out wrong (see the "Dirty Martini" that's only 3 oz. Vodka and 2 oz. Olive Brine) while others are so niche that you'll wonder who submitted them. Thankfully you can rate the recipes and save the ones you like to your favourites list and ignore the rest.
Bartender is free and available now in the Android app market. If you're looking for an app with a smaller database but a more curated approach to drink recipes, try DrinksMaster, also for Android.