You can do that by a new plugin development. You should create a new API using the createUser function  in the /ow_system_plugins/base/bol/user_service.php file.

what about if you just used the same database 

Kieron, we did not design our software the way you want it to be used. Here are some possible problems you may get faced with if you decide to use several copies of the source code and one database:
* All your sites will have one theme and appearance;
* All your sites will have the same settings;
* If someone adds, let's say, status to the Newsfeed, this status will show up for all other sites with the URL the status was added from. The same problem will occur with the Notification plugin, and we are not sure how other plugins will work with this system;
* A new plugin installed onto one site - may not work for the other sites;
* and a lot of other things that we cannot predict.
So, the best way is creating an API that will manage all the users' data and share it between all other sites.

Daisy many thanks I will have a look.

Any devs out there want to give me a few clues.

I am a pretty good dba but groan when it comes to php. :) I should take the plunge I know.

Might fudge it and do a trigger to add the user :)

PS Daisy, Hi how you doing?

:)

Stuart, you are welcome. Please let us know if there’s anything further we can do for you.

Can you possibly give a code example how to connect (synchronize) site1.com and site2.com via a new API using the createUser function  in the /ow_system_plugins/base/bol/user_service.php file?

Alex, unfortunately we cannot provide the step-by-step instructions on how to perform modifications. Please read this topic: http://www.oxwall.org/forum/topic/6082

If you are not familiar with the plugin development, it would be better for you to find a developer who can help you with this plugin development.