This specific virtual journal club (via #TwitJC) is a Twitter-based chat forum for doctors, medical students and others who are interested in research and clinical practice.
In spite of the recent noise about it, it’s not the first one. I fell over a blog post claiming that the first medical journal club on Twitter (or any specialty) was launched back in 2008. And there has been journal club chat rooms on other platforms, e.g., one through the The Stack Exchange Network and the Science and Society Journal Club organised by the Duke Institute for Genome Sciences & Policy (IGSP). There may have been several others (historians of contemporary social media: please fill in the details!)
In retrospect it’s astonishing that so few have found out to use Twitter as a virtual journal club medium. You miss the tea and cakes, of course (which is part of the charm of the traditional journal club), but on the other hand Twitter very efficiently forces participants to shut up after 140 keystrokes. Not a bad idea at all.