Scrum is an iterative and incremental Agile framework for managing projects and product or application development. Its focus is on "a flexible, holistic product development strategy where a team works as a unit to reach a common goal" as opposed to a "traditional, sequential approach" (Waterfall) where the product is a conventional product or the meaningful outcome required by the client.
Scrum acknowledges that the client can change its mind during a project (requirements churn), and that unpredicted challenges cannot be easily addressed in a traditional predictive or planned manner. As such, Scrum adopts an empirical approach¯accepting that the problem cannot be fully understood or defined, focusing instead on maximizing the team's ability to deliver quickly and respond to emerging requirements.
Many practitioners use universally available tools (e.g. MS Excel) to build and maintain artefacts, such as the sprint (time-boxed effort) backlog. There are also open-source and proprietary packages dedicated to management of products under the Scrum process. It is possible (and quite popular in some circles) to implement Scrum without the use of any tools, and maintain artefacts in hard-copy forms such as paper, whiteboards, and sticky notes.