Ab initio methods based on density functional theory (DFT) and non-equilibrium Green functions (NEGF) are an increasingly popular approach to transport properties of nanoscale systems. SMEAGOL is an efficient implementation of such methods, which uses the Hamiltonian provided by the DFT code SIESTA and employs NEGF to calculate the density matrix, transmission coefficients and I-V characteristics. Over 100 groups worldwide have used SMEAGOL to perform simulations of molecular-electronic and graphene-based systems, including insulating and conducting molecules between magnetic, non-magnetic or superconducting leads and molecules encapsulated in carbon nanotubes. As examples of SMEAGOL-based calculations, in this talk I shall discuss a range of geometrical methods for controlling electron transport through single molecules. As well as the control of electrical currents via geometry, the inverse effect is discussed, whereby the geometry of a nanoscale conductor is controlled an electrical current. This is exemplified by carbon-nanotube windmills, whereby an electrical current causes an inner chiral tube of a double-wall nanotube to rotate.