Digital Library Management Systems are systems that are able to manage collections of digital documents that form Digital Libraries and Digital Archives, and they are currently in a state of evolution. Today, most of the times they are simply places where information resources can be stored and made available, whereas for tomorrow they are becoming an integrated part of the way the user works. To cooperate towards reaching this new type of system, a digital library management system must become a tool that constitutes an active part of the intellectual production process.Annotations are effective means in order to enable an effective interaction between users and digital library management systems, since they are a very wellestablished practice and are widely used. Annotations are not only a way of explaining and enriching an information resource with personal observations, but also a means of transmitting and sharing ideas in order to improve collaborative work practices. Furthermore, annotations represent a bridge between reading and writing, that facilitates the user's first approach when they begin dealing with an information resource. Thus, a service able to support annotation capabilities of collection of digital documents can be appealing to the user's needs.This paper presents the main features of a flexible system capable of managing annotations in an automatic way in order to support users and their annotative practices. Indeed, a flexible architecture allows the design of a system with a widespread usage, so that users can benefit from its functionalities without limitations due to the architecture of a particular system. We named this system Flexible Annotation Service Tool and this paper is devoted to introduce most relevant design choices and characteristics of it.