Timesheet software is a group of software that allows its users to track how they spent their time working. It allows them to track how much time and thus budget has been spent on a certain task or project.

Timesheet software allows tracking of time spend for a task (this is the relation to todo lists), the budget spent on a project (important for knowledge workers that bill their customers based on time spent) and allows for better estimates (how much time has been spent for similar tasks in the past) and can be used to some extend to measure knowledge worker productivity.