Experimental cognitive psychology has been greatly assisted by the development of general computer-based experiment presentation packages. Typically, however, such packages provide little support for running participants on different computers. It is left to the experimenter to ensure that group sizes are balanced between conditions, and to merge data gathered on different computers once the experiment is complete. Equivalent issues arise in the evaluation of parameterised computational models, where it is frequently necessary to test a model's behaviour over a range of parameter values (which amount to between-subject factors), and where such testing can be speeded up significantly by the use of multiple processors. This paper describes Express, a web-based technology for co-ordinating ``clients'' (human participants or computational models) and collating client data. The technology provides an experiment design editor, client co-ordination facilities (e.g., automated randomised assignment of clients to groups such that group sizes are balanced), general data collation and tabulation facilities, a range of basic statistical functions (that are constrained by the specified experimental design), and facilities to export data to standard statistical packages (such as SPSS). We report case studies demonstrating the utility of Express in both human and computational experiments. Express may be freely downloaded from the Express website.