Using an innovative approach based on Yb:fiber amplifiers and pre-shaped pulsed diode seeders, a unique laser source with tunable pulse duration and rectangular pulse shape has been developed. Based on the patented use of multimode fibers with single-mode output, the resultant system provides pulses adjustable between 4 and 20 ns duration with sharp rise times of < 1.5 ns, at a repetition rate of up to 20 kHz. The output pulse energy of > 15 microJoules can be maintained over the full tuning range. The high-quality output beam is coupled into a polarization-maintaining, single-mode delivery fiber for ease of integration into an application. With this "tailorable" pulse design, control of laser energy deposition in very confined laser interaction zones (by pulse shape), and of its dosage (by pulse duration) can be optimized by the user and adjusted in real-time from the laser controller in response to measured structural changes. Results of machining of materials such as Si, Cr on glass and drilling of Cu/Pl/Cu are presented, showing the unique capability of this laser and its advantageous use to ablate, structure, repair, or trim very small areas (down to sub-micron size) without damaging or influencing the underlying and/or neighboring structures.