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They are commonly known as "console cables" or Rollover cables. They are NOT Ethernet! They are often flat CAT3, or just 8 conductor ribbon cable. All console cables are null modem cables, it is just the pin out that is sometimes different.
You'll sometimes hear the term "silver satin" cable (Crossed / Straight).

Crossed Straight
Any ideas on what type of cables these are?
Cable 1
cb75414d-48ba-419b-94e5-b130b819cfe0-cable1-edit.jpg800×355 88.8 KB
Cable 2
f9b615e3-b37d-46ff-ad8b-a8b503bc19a4-cable2-edit.jpg576×768 149 KB
Cable 3
aad7cfd5-4db9-459d-9aac-97a0147cf443-cable3-edit.jpg800×355 97.5 KB the top cable is a DB15 splitter. Game controllers in the 90’s before USB used DB15.
the second cable is a serial cable. most likely for a router or switch console connection, but i have seen them to connect motherboards to sensors and other equipment in specialized equipment, like inside a treadmill to connect the console.
Yes - I would call that a Null Modem cable.
If the cable you get (or make) doesn't work, my first debugging step for serial communications is to swap connections on pins 2 and 3. (Transmit and Receive data)
Since the TXD (3) of one side is connected with the RXD (2) of the other, this is indeed a null-modem cable. Normal serial cables have pins 2 and 3 connected straight through, and the DCE is responsible for cross-connecting them internally.