In reviewing some of the data published by the FAA, I noticed that they make a distinction between a mechanic certificate and a repairman certificate. What is the difference?
The basic difference is that a mechanic can perform maintenance on any aircraft; a repairman can perform maintenance only on aircraft for their employer, or that they own.
A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95.
A certificated repairman may perform or supervise the maintenance, preventive maintenance, or alteration of aircraft or aircraft components appropriate to the job for which the repairman was employed and certificated, but only in connection with duties for the certificate holder by whom the repairman was employed and recommended.
"Repairman" also applies to experimental and light sport aircraft owners. If you build your own aircraft you have repairman privileges to maintain it, but you can't use those privileges to work on other aircraft, per 65.104(b) (emphasis mine):
The holder of a repairman certificate (experimental aircraft builder) may perform condition inspections on the aircraft constructed by the holder in accordance with the operating limitations of that aircraft.
This page from the FAA discusses both
I'm a US Citizen. What requirements must I meet to get a mechanic's certificate?
You must be at least 18 years old;
able to read, write, speak, and understand English.
You must get 18 months of practical experience with either power plants or airframes, or 30 months of practical experience working on both at the same time.
As an alternative to this experience requirement, you can graduate from an FAA-Approved Aviation Maintenance Technician School. You must pass three types of tests;
a written examination
an oral test
a practical test
How do I get a repairman's certificate?
To get a repairman's certificate, you must be recommended by a repair station, commercial operator, or air carrier. You must
be at least 18 years old;
be able to read, write, speak, and understand English
be qualified to perform maintenance on aircraft or components
be employed or a specific job requiring special qualifications by an FAA-certified Repair Station, commercial operator, or air carrier.
be recommended for the repairman certificate by your employer
have either 18 months practical experience in the specific job or complete a formal training course acceptable to FAA.
So they look similar, with one having testing to go with it.