In this paper, we introduce new process control facilities in the ELAN language as low-level primitives and high-level concurrent strategies. The low-level primitives are similar to those existing in UNIX for process control and communication. The high-level concurrent strategies proposed in this paper extend their existing sequential version giving them a new behaviour while preserving their operational semantics. This extension of the ELAN language allows to prototype in a very abstract and flexible way the integration of several computational systems within the same rewriting framework. Using the high-level concurrent strategies we can also avoid some non-terminating processes and/or apply the most efficient rewrite rule or strategy. We exemplify their use by prototyping different kinds of cooperation between constraint solvers, e.g. sequential and concurrent solvers.