Condor is a high-throughput batch job system. It works well in both local and grid environments. In a local environment, Condor can utilize dedicated clusters of computers, or non-dedicated computers like the workstation on your desktop. In a grid environment, you can link Condor pools together with Condor-C or flocking, or you can submit jobs to other types of grids, such as Globus, using Condor-G.
Condor is more flexible than many users realize. For instance, Condor has sophisticated to control batch job scheduling. (See, for example, the Bologna Batch System.) Condor also has sophisticated user job policies to allow users to say things like, "If my job runs for more than 10 hours, kill it because something is wrong.". In addition to independent jobs, Condor can run MPI programs.