Gantt chart (or bar chart) is a popular tool for developing and displaying job schedules. This paper focuses on software that provides a Gantt chart interface to enable users develop job schedules interactively. Here the Gantt chart is not merely a display format; the chart is used to develop and manipulate a jot schedule. The user can point at different parts of the chart and indicate his requirements. The main features that the paper discusses are forward and backward scheduling of a job, shifting a scheduled operation, interactive specification of heuristics, and Gantt chart colouring. Representation of a Gantt chart by suitable data structures is very important for an efficient implementation of these features. The paper also focuses on the data structures useful in implementing some of the above features.