screen-scraper automates:
Clicking links on websites
Entering data into forms and submitting
Iterating through search result pages
Downloading files (PDF, MS Word, images, etc.)

Common uses:
Download all products, records from a website
Build a shopping comparison site
Perform market research
Integrate or migrate data

Technical:
Graphical interface--easy automation
Cross platform (Linux, Mac, Windows, etc.)
Integrates with most programming languages (Java, PHP, .NET, ASP, Ruby, etc.)
Runs on workstations or servers