there are two options:
standard based workflow  engines
non standards
there are various standards for workflow, the best one is from
wfmc.org and the worst is bpel.
if the workflow will be used only internally standard  based workflow
engines are very limited. you may use other engines which have their
own language  and design idea.
jBPM from jboss is one of those you can find several others by a few
search in google and other search engines.
serveral of them are hosted on source forge.
if your customer is in iran you can also user commercial procuts which
are likely much better than most of their open  source counterparts.