Three collider concepts are presented: the 7-on-32 GeV e-p and the
10-on-250/100 GeV e-p/A ring-ring colliders, and the 10-on-250/100 GeV e-p/A
linac-ring collider. Their basic limitations and potential luminosities are
assessed and compared as well as schemes for beam polarisation and electron
cooling of the hadron beams.