I started doing Pomodoros [1] recently and I noticed a leap in my productivity. It also helps me to refresh my mind regularly and to stay focused on my tasks more easily.
I can credit it with getting me through seven novel drafts, through a successful Kickstarter campaign, and even with helping me find this new, much better-paying job.
Best part about pomodoro? How easy it is to begin using it!! You don't need a lengthy book or a long lesson. It is just as simple as using the damn timer.
I don't know why I became lazy and stopped using it. When I tried it for a week I was definitely at a higher bound of productivity for my school work. Totally helped me to gain more time to focus on my own projects. Time to start up again.
not sure if it qualifies as "a good mac app"