Which of the following is not an operating system software?

MS Office is not an operating system software. MS Office, which stands for Microsoft Office, is a suite of productivity applications developed by Microsoft. It includes applications such as Microsoft Word, Microsoft Excel, Microsoft PowerPoint, and others. MS Office is not an operating system software; rather, it is an application software used for word processing, spreadsheets, presentations, and other office-related tasks. The other options listed (Windows, Linux, and Ubuntu) are operating system software. They are the core software that manages computer hardware and provides services and functions for computer programs and users. Windows is a popular operating system developed by Microsoft, Linux is an open-source operating system, and Ubuntu is a popular Linux-based operating system distribution.