We present a Brownian inchworm model of a self-propelled elastic dimer in the absence of an external potential. Nonequilibrium noise together with a stretch-dependent damping form the propulsion mechanism. Our model connects three key nonequilibrium features -position-velocity correlations, a nonzero mean internal force, and a drift velocity. Our analytical results, including striking current reversals, compare very well with numerical simulations. The model unifies the propulsion mechanisms of DNA helicases, polar rods on a vibrated surface, crawling keratocytes and Myosin VI. We suggest experimental realizations and tests of the model. While not losing sight of the application to particular organisms or devices, our focus is on the general principles governing propulsion by rectification of an unbiased input active noise in a homogeneous medium.In all the systems mentioned above, macroscopic directed motion of the center-of-mass (CM) arises via a coupling to internal coordinates, as a result of two crucial features -an asymmetrical environment for the internal coordinates and external energy input. Unlike in traditional "Brownian ratchet models" [8] of directed motion, the asymmetry of interest in the above systems is internal to the motile objects, and does not lie in an external periodic potential. Our approach is distinct from that of [9] where the external potential plays a central role, and also differs from the dynamical systems approach of [10]. The present model is similar in spirit to [11,12] but simpler, and differs in several important details as seen below. We find an unexpected range of possible behaviors, especially in the dependence of the motion on the details of the nonequilibrium noise.Our model self-propelled object is a dimer whose two heads are coupled by a spring, in a homogeneous, dissipative, noisy environment. The damping coefficients of the heads depend on the relative coordinate or strain. The noise on the particles is made of two parts -a thermal part whose strength is determined by a fluctuationdissipation relation with the strain-dependent damping, and a nonequilibrium or active part, with strength independent of the damping, which represents the external energy input.Our results are as follows: (i) The steady-state average of the CM velocity is in general nonzero and exhibits counter-intuitive reversals of direction as a function of the strengths and characteristics of the drive and the dampings. (ii) The steady state displays two other key nonequilibrium features: the mean internal force as well as the the equal-time correlation of the relative coordinate to the CM velocity are both nonzero. (iii) Active noise alone will not result in propulsion, even in the presence of an asymmetric internal potential; the straindependent damping is an essential ingredient. (iv) The preceding results, obtained by perturbative analytical solution of our model Langevin equations, with the coefficient of the stretch-dependent damping as a small parameter, are confirmed in detail by direct numerica...