Quicklaunch Ultimate Edition provides enterprise-level integration with Skype for Business, which utilizes an Windows Active Directory account. If the Quicklaunch PC is external to the organization network and the Skype for Business account has access to the Skype for Business infrastructure as an external user, then there is no need for the Quicklaunch PC to be joined to a Windows Domain. Using a Skype for Business account on an internal corporate network requires certificates to be installed, which is typically satisfied by joining the PC to the network.
Quicklaunch Standard Edition does not provide Skype for Business integration and does not have any requirements for a Windows Domain account. It will work with either an Active Directory or Local Computer user account.