Calendars

"A schedule or timetable is a basic time management tool consisting of a list of times at which possible tasks, events, or actions are intended to take place, or a sequence of events in the chronological order in which such things are intended to take place. The process of creating a schedule - deciding how to order these tasks and how to commit resources between the variety of possible tasks - is called scheduling, and a person responsible for making a particular schedule may be called a scheduler. Making and following schedules is a fundamental human activity, and learning to do these things effectively is one of the most basic life skills. There are a wide variety of situations in which schedules are necessary, or at least useful.
Schedules are useful for both short periods, such as a daily or weekly schedule, and for long term planning with respect to periods of several months or years. They are often made using a calendar, where the person making the schedule can note the dates and times at which various events are planned to occur. Schedules that do not set forth specific times for events to occur may instead list an expected order in which events either can or must take place." [Schedule. Wikipedia]
The UML sequence diagram example "Checking process" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Rapid UML solution from the Software Development area of ConceptDraw Solution Park.