While searching the web this week I came across a link to the Turing Pi/Pi2. See Turing Pi
Basically the Turing Pi is an mITX board that you plug a number of Raspberry Pi Compute Modules (CM) into. It holds up to 7 CM, CM2, CM3 or CM3+ modules. The Turing Pi2 is a rework of that design to use the Compute Module 4 which is based around the Raspberry Pi4 SoC and has slots for 4 CM4 modules. This should be great for a cluster of Pis when its released.
While looking there I ran across a video clip from Jeff Geerling explaining what the Turing Pi is which then led me onto his other Raspberry Pi videos. I had heard of Jeff but wasn't aware he also has a YouTube channel. I had a look at his series called Ansible 101 on a Pi cluster which I will try soon. See Ansible 101
In other Raspberry Pi news last week they introduced the Pi400 which is a reworked Pi4 built into a Raspberry Pi keyboard. All the connectors are at the back of the keyboard. Jeff has a video where he does a tear down on a Pi400. Unlike the Pi4 model B its clocked at 1.8Ghz (the Pi4 model B is 1.5Ghz) and has a large heatsink spread across the width of the keyboard. I expect this means we will see a Raspberry Pi4 model B+ soon.