A free program for Android, by SC2 Tools Lab.

This is a great app for creating build orders, as well as managing your units and resources. You can use it on your smartphone, so you will never lose your data. The interface is easy to use, so even if you have never used a game development application before, you will be able to learn how to create a build order in less than a minute. You can also learn how to craft a specific type of weapon, or armor, for example. If you want to know more about how the game works, you can also read the in-game help. You can use the app on the PC as well, but in that case, you will need to install the official client.