Follow the Leader: Received one in the early 2000's in the form of Code Head, a pair of Edutainment games that played extremely similar to YDKJ; X-Treme Culture, which taught language arts and grammar, and Calculated Risk, which taught mathematics. Both games featured Dee Bradley Baker as host and featured similar question types from YDKJ.
Keep Circulating the Tapes: The Webshow, which ran on Jellyvision's website from early 2007 to late 2008, is long gone (having been taken down upon the release of 2011). However, all 100 episodes have been archived and are available for download, though certain features (such as leaderboards) understandably don't work.
Name's the Same: Host Nate Shapiro shares a name with Nate, the intern from The Webshow.
The Other Darrin: Quizmaster Jack was voiced by Axel Malzacher in Volume 1 in Germany, then in the other four iterations of the German localization he was voiced by Kai Taschner.
Real-Life Relative: Jellyvision founder Harry Gottlieb voiced Nate Shapiro, the original host. His brother Tom voiced sign-in guy and eventual Ascended Extra Cookie Masterson.