Web Self Service (retired with the launch of XenServer 6.2) was a lightweight portal which allowed individuals to operate their own virtual machines without having administrator credentials to the XenServer host. For large infrastructures, OpenStack is a full orchestration product with far greater capability; for a lightweight alternative, xvpsource.org offers a free open source product.

Related Citrix products have browser based access, for example Storefront (next generation of Web Interface)

XenOrchestra is a web interface to visualize and administrate your XenServer (or XAPI enabled) hosts. No agent is requiered to make it work. It aims to be easy to use on any device supporting modern web technologies (HTML 5, CSS 3, JavaScript) such as your desktop computer or your smartphone. More info: https://tinyurl.com/ya7d72q6