Nowadays a lot of people are keen to make presentations on computer to express their ideas. For example: teacher uses PPT and Flash to make courseware, financial staff uses it to show reports, designer demonstrates conception, and so forth. But presentation based on slideshow is missing the interaction and convenience of the traditional blackboard/whiteboard, which leads to such a bad result that both lecturers and audiences can only passively march forward following the scheduled architecture. This seems to be efficient, but is actually not as free and flexible as "a piece of paper + a pen".