Basic, but a must. It is synced on all my devices which is really helpful and I can quickly see what I have going on that day and plan around it.
I love this app. I just recently downloaded it and have been using it ever since. If you download one app on this list, make it this one (cause you probably already have the others). I love that I can pick how long I want to do an activity for and it will cycle through my list and alert me when time is up. When I am studying I will usually just set it on a simple study for 50 minutes, break for 10 schedule.
I can't listen to music with lyrics when I study but sometimes I need some background noise. I love the different classical playlists for this. They help me focus on what I am studying without getting distracted.