Tethers are an underutilized tool in systems composed of many robots which generally try to fit simple, cost-effective hardware to complex collaborative tasks. Tethers (of fixed- or variable-length) can function as both a sensor and control input, and a physical mechanism for simplifying and accomplishing collective tasks. This dissertation presents a multi-robot system composed of agents tethered in series by flexible, un-reeled tethers, where each tether is capable of sensing the magnitude and direction of tension. Each agent uses the measured strain in the tethers to inform motion according to competing objectives which include keeping the tethers taut and reaching a user-specified angle difference between them. Although agents act asynchronously, do not communicate, and are restricted to close-range sensors, the collective is still able to achieve formation control, navigate cluttered environments using gradient-following, and can encapsulate or gather and transport objects. Reported results were examined in simulation and briefly demonstrated on a proof-on-concept platform. The proposed algorithm is well-suited for simple tethered agents collaborating in environments where communication and/or visibility is constrained, (e.g. unmanned underwater and subterranean vehicles, or micro-scale robot collectives in bio-medical applications) and could also act as a backup mechanism for more capable robots.