Movable-axis hinge for furniture doors and the like, comprising: - a first coupling unit connectable to a fixed part of a piece of furniture or the like; - a second coupling unit connectable to a moving part of a piece of furniture or the like; a kinematic movement mechanism interposed and hinged between said first coupling unit and said second coupling unit and capable of reversibly configuring said moving part between a closed state and an open state and comprising a first pivot and a second pivot connected to the first coupling unit, a first arm mounted rotatably on said first pivot and having a third pivot at one of its ends opposite said first pivot, and a second arm rotatably mounted on said second pivot and having a fourth pivot at one of its ends opposite said second pivot, the second coupling unit being rotatably connected to said third pivot and said fourth pivot; and - an assistance device that acts, operationally, on said kinematic movement mechanism and is reversibly configurable between an assisted closing state, in which it exerts an action of drawing back the moving part towards the fixed part, and a stable state in which it exerts at least an action of holding the moving part in position at at least a given angle of opening with respect to the fixed part, the assistance device comprising an elastic reaction unit developing axially interposed operationally between said first arm and said second arm, said assistance device further comprising a support sleeve and a support stem partially penetrating into each other and capable of supporting the elastic reaction unit at opposite ends, characterised in that a first coupling foot emerges from one end of said support sleeve and capable of engaging, preferably via a socket, with the first arm or the second arm, and a second coupling foot emerges from one end of said support stem and capable of engaging, preferably via a socket, with the second arm or the first arm. - a first coupling unit connectable to a fixed part of a piece of furniture or the like; - a second coupling unit connectable to a moving part of a piece of furniture or the like; a kinematic movement mechanism interposed and hinged between said first coupling unit and said second coupling unit and capable of reversibly configuring said moving part between a closed state and an open state and comprising a first pivot and a second pivot connected to the first coupling unit, a first arm mounted rotatably on said first pivot and having a third pivot at one of its ends opposite said first pivot, and a second arm rotatably mounted on said second pivot and having a fourth pivot at one of its ends opposite said second pivot, the second coupling unit being rotatably connected to said third pivot and said fourth pivot; and - an assistance device that acts, operationally, on said kinematic movement mechanism and is reversibly configurable between an assisted closing state, in which it exerts an action of drawing back the moving part towards the fixed part, and a stable state in which it exerts at least an action of holding the moving part in position at at least a given angle of opening with respect to the fixed part, the assistance device comprising an elastic reaction unit developing axially interposed operationally between said first arm and said second arm, said assistance device further comprising a support sleeve and a support stem partially penetrating into each other and capable of supporting the elastic reaction unit at opposite ends, characterised in that a first coupling foot emerges from one end of said support sleeve and capable of engaging, preferably via a socket, with the first arm or the second arm, and a second coupling foot emerges from one end of said support stem and capable of engaging, preferably via a socket, with the second arm or the first arm.