OpenjACOB as provided by Tarragon gives you all the design functionality of jACOB Enterprise.  If you design your applications witrh OpenjACOB and at some later stage wish to transfer your design to the enterprise version you can do so without having to change a single item of your application. The reverse is also possible.

Enterprise versions run on a number of different databases and  on server clusters. OpenjACOB doesn't and that is all that there is to it.