Keycard and fob systems present a credential to a reader instead of a mechanical key. The card or fob carries an identifier, the reader sends it to a controller, and the controller decides. The practical difference between products is the credential technology and how it is protected from copying.
A building usually ends up with one credential format. Choosing it early is cheaper than running two reader types on the same corridor for years.
The common card types
Magnetic stripe, 125 kHz proximity and 13.56 MHz smart cards are the main families. Only the last supports mutual authentication and encrypted data on the card.
Wiegand and OSDP
Wiegand is the long-standing reader-to-controller protocol and sends data unprotected. OSDP is the newer serial standard with encryption, and most new work should use it.