Hello,
You can create a simple web service or WCF service. you have to deploy this service to any particular server and share details with clients.
Using WCF you can return data in mode of XML or JSON and if making simple web service then they can also get the dataset or datatable.
Its up to you what provision you need to give them.
How to create web services (WSDL),
http://www.w3schools.com/webservices/ws_example.asp[
^]
How to create WCF services (VCF),
http://wcftutorial.net/[
^]