LOFT, the Large Observatory For X-ray Timing, is a newly proposed space mission intended to answer fundamental questions about the motion of matter orbiting close to the event horizon of a black hole, and the state of matter in neutronstars.
LOFT was selected by ESA as one of the four M3 space missions concepts of the Cosmic Vision programme. LOFT was not selected as the final M3 or M4 mission to be lauched on the 2020s. 
Why X-ray timing?
High-time-resolution X-ray observations of compact objects (as the Galactic and extraGalactic neutron stars and black holes) provide a unique tool to investigate strong-field gravity, and give direct access to measurements of black hole masses and spins, and to he equation of state of ultradense matter.
A 10 m2-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two fundamental questions of ESA's Cosmic Vision Theme Matter under extreme conditions, namely:
Does matter orbiting close to the event horizon follow the predictions of general relativity?
What is the equation of state of matter in neutron stars?

Thanks to an innovative design and the development of large monolithic silicon drift detectors, the Large Area Detector (LAD) on board the Large Observatory For x-ray Timing (LOFT) achieves an effective area of ~10 m2 (more than an order of magnitude larger than current spaceborne X-ray detectors) in the 2-30 keV range (up to 80 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of <260 eV over its entire band, LOFT will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei, yielding unprecedented information on strongly curved spacetimes and matter under extreme conditions of pressure and magnetic field strength.