  We propose the simplest model of teleparallel dark energy with purely a
non-minimal coupling to gravity but no self-potential, a single model
possessing various interesting features: simplicity, self-potential-free, the
guaranteed late-time cosmic acceleration driven by the non-minimal coupling to
gravity, tracker behavior of the dark energy equation of state at earlier
times, a crossing of the phantom divide at a late time, and the existence of a
finite-time future singularity. We find the analytic solutions of the
dark-energy scalar field respectively in the radiation, matter, and dark energy
dominated eras, thereby revealing the above features. We further illustrate
possible cosmic evolution patterns and present the observational constraint of
this model obtained by numerical analysis and data fitting.
