In recent years, the Space Debris field has gained a lot of attention due to the growing population of uncontrolled objects orbiting the Earth, causing an increase in the risk of collision with operational satellites. A clear example of this interest is the European Space Situational Awareness (SSA) initiative. As part of GMV's activities in this field, GMV has developed closeap, a tool for conjunction assessment, collision probability prediction and collision avoidance manoeuvre optimization integrated in focusSuite, GMV's commercial off-the-shelf (COTS), multi-mission, multi-satellite flight dynamics solution for satellite control. closeap is based on the already mentioned CRASS and ODIN tools and also on ESÁs NAPEOS software (Navigation Package for Earth Orbiting Satellites). This paper presents closeap as a flight dynamics application to support satellite operations for collision risk assessment tasks. On the one hand, the paper focuses on its design and inheritance from other existing software packages, as well as on the performances obtained in real conjunction scenarios. On the other hand, an overview of the algorithms implemented in closeap is also carried out, even though most of them are described more in detail in the literature.