Absolutely. Marvin can also be used solely as a day planning tool. Each day you can make a daily todo list with Marvin - pulling tasks from another application or even paper planners. Marvin offers many features that can help you not only plan a great day but also work off those tasks (super focus mode, timers, time estimates, sectioning your day etc.). So it has a lot of benefits even if you use another application to store your tasks/projects (e.g. Todoist, Wunderlist, Trello, Asana etc.)