The Gemini Observing Tool (OT) is the software used for detailed definition and planning of observations from approved proposals during the Phase II process. The OT is also the high-level interface for on-site (classical and staff) observers. It supports observations with all facility instruments (visiting instruments normally have their own control systems and are not integrated with the high-level software).
The philosophy of the OT is to hide the complexity of the Gemini Observatory control systems (e.g. 60+ TCS and sub-system engineering control screens) and yet not restrict significantly the scientific capabilities and innovative observing techniques. It is intended to be the sole instrument user interface (at the telescope as well as remotely), capable of configuring and sequencing instrument and telescope motions and integrating the data processing pipeline with data taking.
Assistance with its use can be found at the OT Help pages.
You can also access a description of all of the OT's components, and their function.