信呼是一套免费开源的协同办公系统，为各大中小企业通用型在线办公管理系统，精简，便捷方便使用的管理软件，让每个企业单位都有属于自己的办公系统。(The letter is called collaborative office system a free and open source, down to the small and medium-sized enterprise universal online office management system, convenient use, c