I found this in JD's ROM thread...I thought it would be helpful for hte entire community:
http://forum.ppcgeeks.com/showpost.p...&postcount=983
1.COM2 this branch has the older UI but is more stable in terms of functionality and I feel like this may be the branch that HTC uses for their upgrade to 6.5 - this branch includes the .5.0.xx aku posibly leading up to 6.5.0.1 - which is made up of the builds 218xx the last build from this branch is 21857.5.0.66
2.COM3 this branch introduces the features from the MSFT development branch that is stable enough to merge with COM2 and starts the experimental development of newer UI code this branch includes the aku of .5.3.0 builds from this branch are 230xx the latest build from this branch is 23053.5.3.0
3.COM4 this branch will merge the stable new UI code with an updated OS code and is the development branch for what some will say is the 6.5.1 builds but according to an article that I read when 6.5 goes public there will be two versions and I believe this branch introduces the development of the higher design for MSFT devices builds from this branch will have an aku of .5.4.0 the latest build from this branch is 23414.5.4.0