What is the latest installable version on an original Android G1 phone? Either vanilla or any kind of mod (CyanogenMod, etc).
COS-DS is an Android 2.3 based ROM that I have been running for months on my ADP1 (identical to G1). It runs quite well although applications are starting to struggle with the limited RAM.
There are other 2.3 based ROMs but when I first wanted to switch to 2.3 this was the most stable and I have stuck with it since.
CyanogenMod 7.1 has been unofficially ported to the Dream/Sapphire platform. This is an Android 2.3.5 based ROM with some of the heavy weight bits stripped out. It seems to run just fine on my ADP1.