There will be lots of deals brewin’ on National Coffee Day, Friday, September 29. And here’s one of them: Dunkin’ Donuts is celebrating the (caffeine) buzz-worthy holiday in Colorado with a hot offer. The coffee/donut shop is offering a buy-one-get-one FREE medium hot coffee at participating locations. (The FREE medium coffee also applies, if you purchase a large.) It’s the perfect opportunity to sip coffee with a friend and catch up on life.