I don't think he means an applicant tracking system (ATS) as are used by recruiters and HR. They all suck though (even the paid ones are backwards in a data-science sense and lack intelligence that would now be possible with ML/data-science). And none of those are available as opensource at least not useable ones, so there is lots of room here for something that is transparent and can help harvest intelligence from the web.

I think what OP had in mind was a system that lets the job seeker track what was communicated and sent to a certain company. This is an awesome idea for many reasons: You could track which companies are notorious for failing to provide feedback to job seekers (even negative ones) or even shed light on which ones take ages to respond. It would be awesome to have a transparent infrastructure in place that is cloud based, open source, free, tracks these feedbacks in an "open/transparent" manner. I dislike the idea of tying into gmail (or facebook or google or other third party walled garden systems) though. I'd be happy to help on the technical side with requirements, use-cases and maybe even some funding.

Disclosure: one of my current companies works in recruitment but I have a SW development & infosec background. My profile has my contact details if interested.