Macragge1's Protect and Survive TL has received a remarkable amount of spinoff stories by other AH.com authors, something quite rare for AH.com timelines. Here's a comprehensive list of them, sorted by their primary geographic setting.
The Journey - One-off short story written by JN1. Set in eastern Scotland and focusing on daily life and the importance of surviving railways 23 years after The Exchange, in an alternate 2007. So far, it is the only spinoff that focuses purely on an era years after The Exchange.
Protect and Survive - Report on Germany - Written by Hörnla as a fictional document made by the Swiss government about the post-war situation in the Federal Republic of Germany and the German Democratic Republic.
The Land of Flatwater - The second American spinoff, written by Chipperback. Set primarily in Nebraska and other parts of the midwestern US, with prominent sideplots set in the German/European front of WWIII.
We Served the Soviet Union - A story series with a fictional interview-like format, focusing on former Soviet soldiers that were stranded in North America during The Exchange and were forced to stay there for one reason or another. The interviews present the oral histories of these veterans from the other side of the barricade. The series ties in with The Land of Flatwater, where several of the characters were first introduced. Written by Panzerfaust 150.
No Rest for the Wicked - Set in various countries of Africa, including Lybia, Ghana, South Africa and a plethora of others. Written by Agentdark, with some chapters about southern Africa written by Shurik.
When the Wind Blew : The P&S Open Thread - If you're interested, you can also visit this thread and discuss the original timeline and its steadily growing “expanded universe” of spinoffs.
Protect & Survive in 2012 - Another good discussion, about the possible situation of the P&S universe in the year 2012.