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 call is a set of free open source cooperative office system, for the large and medium and small enterprises general online office management system, streamlined, conven