Rabotan ToDo Calendar, a full-featured all-in-one calendar and To-Do list, is presented by mathematicians of French National Centre for Scientific Research and Russian Academy of Sciences. This handy application for Android is based on the fact that the nature of ToDo tasks and calendar events is essentially the same, i.e. scheduled tasks appear in the calendar views (month, week, day), and an event's status can be changed to "completed", "late", etc.
Rabotan ToDo Calendar is remarkable for automatic interchange of tasks and information about their completion via SMS and email. Now it's quite easy to send a task, e.g., "buy milk" or "send up a report" to a family member or a colleague in two clicks. A short description with a due date will be sent automatically in a special easy-to-read format "task [to report], due date =[09.12.20xx]
To sum up, Rabotan ToDo Calendar makes it quite easy to send a task to someone and to be sure that he/she has received it even without internet access. Other useful features of the app include hierarchical task list view, a flexible fully-customizable task filter, task group editing, task export/import and more.