Where can I get an email program for contact support?

Preferably free, I'm looking for an email-based program that allows me and my wife to answer emails simultaneously without sending an email to the same person. I used to work in a multinational company's contact center, we used this program that acts as a huge Inbox and we just grab some emails so that we don't answer the same email twice. Am sure that was customized, but is there a commercial program out there that I can use? Thanks!