Lots of companies are using automated applicant tracking systems today. Resumazing figures out what changes you'll need to make to your resume to get the job you want.
The web service compares your current resume (or LinkedIn profile) and a job you're interested in getting. It then scores your resume based on the job description. If your score is low (like the one in the picture), Resumazing gives you the keywords you need to include to get a better score. It shouldn't be the only driving force behind your resume, but it's a good check to run at the end.