Workday simplifies your work day by putting all of the tasks that you are assigned to (across tools) in to one easy-to-view feed.
Workday is an app that aggregates all of your work-related tasks from various teams and project management tools in to one place (think: Your trello cards, pivotal tracker stories, asana tasks, google calendar meetings, all in one place ).
Often times, different teams in the same company use different product management tools. Engineeers may use Pivotal Tracker, designers may use basecamp, and product management may prefer Trello; each team choosing the tool that suits their own needs and workflows. This is especially true the larger the company gets.
For collaborators across teams, this makes keeping track of tasks that are assigned to them by different teams difficult, since they have to check multiple tools. Workday aims to simplify this process.