The Orchestrator needs a database in order to be installed on-premises.
As per the documentation provided above by @balupad14:
“A SQL server machine with one of the following versions: 2008 R2 with SP3 as a minimum requirement, 2012, 2014, 2016, or 2017 Standard or Enterprise Edition.”
UiPath Orchestrator is a web application that enables you to orchestrate your UiPath Robots in executing repetitive business processes.
Orchestrator lets you manage the creation, monitoring, and deployment of resources in your environment, acting in the same as an integration point with third-party solutions and applications.