Cluster proposes a universe composed of spheres of influence, in which Sol's is still pretty tiny. Travel is slow and sublight for the most part, but objects and people can be "mattermitted" at great cost. The cheapest way to travel is to project one's Kirlian aura (essentially the life force) into a host body. This is relatively cheap in terms of energy and instantaneous (as far as we allow for simultaneity across big-ass frames of reference), but an aura away from its "home" body fades and must return or become the host body and soul. This allows the characters to know what it's like to be, for example, a Polarian, a Solarian, etc. It's also pretty fun to read.