Watchman Monitoring reports how many and what size chips are installed. If a computer's RAM size unexpectedly drops by 50% it is usually a sign one of the RAM chips is going, or has gone, bad. POST test results are also likely to find bad RAM chips. Watchman Monitoring uses the OS's built in memory check, this captures the worst of RAM errors, as well as any ECC issues in Mac Pros.
The RAM Errors plugin also reports ECC status if the computer is using ECC RAM.
Example ECC Error