The electronic transport in independent Double-Gate nanotransistors is theoretically investigated using a self-consistent Poisson-Schrodinger solver based on a two-dimensional (real-space) Non-Equilibrium Green's Function (NEGF) approach and parallelized code architecture. Physical insights concerning the three- and four-terminal operations of these independent-gate devices are provided for long-term technology nodes (5-10 nm channel lengths) and pure ballistic operation.