[luckystrike]

You can have a look at Resumonk - https://www.resumonk.com

The paid plan allows creation of multiple resumes/cover letters each customized for a particular job opening. It gives a 'Clone' option that creates a copy of the existing resume and you can then tweak it based on the job you are applying. All these versions of your resume/cover letter are available from your Dashboard for future reference.

Full Disclosure: I'm the Co-Founder of Resumonk.