  The ideal laser source for the emerging research field of nonlinear Terahertz
(THz) spectroscopy should offer radiation with a large versatility and deliver
both ultra-intense multi-octave spanning single-cycle pulses and
user-selectable multi-cycle pulses at narrow linewidth. The absence of such a
table-top source has hampered advances in numerous THz disciplines including
imaging, nonlinear photonics and spectroscopy, selective out-of-equilibrium
excitation of condensed matter and quantum systems. Here we introduce a highly
versatile table-top THz laser platform providing single-cycle GV/m transients
as well as spectrally narrow pulses tunable in bandwidth and central frequency
across 5 octaves with hundreds of MV/m field strength. The compact scheme is
based on optical rectification of a temporally modulated laser beam in organic
crystals. It allows for the selection of THz oscillation cycles from 1 to >50
and central frequency tuning range from 0.5 to 7 THz by directly changing the
modulation period of the driving laser. The versatility of the THz source is
demonstrated by providing a broadband 5-octave spanning spectrum as well as a
spectrally narrow line tunable across the full optical rectification
phase-matching band with a minimum width of dv=30 GHz, corresponding to dE=0.13
meV and lambda^-1=1.1 cm-1. The presented table-top source shows performances
similar or even beyond to that of a large-scale THz electron accelerator
facility but offering in addition versatile multi-color and advanced
femtosecond pump-probe opportunities at ultralow timing jitter.
