The first app, and maybe the best, is Evernote. This a free application with which you can easily organize your time, write your ideas and notes. Also, the application offers photography, creating "to-do" list, audio recording and more.
Also, another great option which is offered by Evernote is the synchronization several devices, so, you can everywhere and at any time check your notes, ideas, photos.
Wunderlist Task Manager is also а free applications and great task manager. With the help of Wunderlist you can create and organize lists in categories, share them with your friends, and like Evernote, you can synchronize it with a number of devices.
Google Drive is a bit different from the previous two, but it's very useful to have it on your smartphone. It offers you several gigabytes of free space in the cloud, and you can use that to put all your presentations and documents from college.
Also, if you are working with a colleague on a project, you can together prepared it in real time.