These are the CMSR's Fold3 currently has available:
Confederate - Soldiers from units in all states, non-state Confederate units, Confederate Officers, Confederate Miscellaneous, Confederate citizens files, etc.
Union Records from States: California, Massachusetts, Oregon, Vermont, West Virginia, Delaware, Kentucky, Missouri, Maryland, Colorado, Dakotas, Utah, New Mexico, Nevada, Nebraska and District of Columbia
Union regiments formed in: Alabama, North Carolina, Texas, Virginia, Tennessee, Mississippi, Louisiana, Georgia, Florida
USCT, 1st NY Engineers, and Naval Officers
It's important to know that CMSR's are collections of carded records filed by soldier. Rosters, rolls, logs, etc. were transcribed to "cards" (hence the name "carded records") and filed by soldier in the late 1800's and early 1900's to facilitate verification of service and pension processing. In many cases, they are not copies of the original document. For example Company Muster Rolls are just the transcribed info from the actual roll. If there's card for a hospital admission included - it's not the actual daily log or roster. Those entries were transcribed to individual cards and filed in the soldiers' CMSR, by name.