Having a look at the boards and with some guessing, we can say some things about the different versions.
Most of the cards have a gate array for interfacing an Ethernet controller with the ISA bus and allowing the PC to control the device. The gate arrays come in a few different versions and in more than one case is marked as an AT&T made part.
If you fancy a go at programming the Etherlink II you can download the manual here.
Etherlink I
Gate Array: 0755-02Ethernet Controller: SEEQ DQ8001 EDLC Etherlink Data Controller (this appears to be where the name Etherlink orginates from in the series).
Etherlink I 16
Gate Array: Xilinx (FPGA?)Ethernet Controller: Intel N82586
Etherlink II Rev A
Gate Array: 3588-01
Ethernet Controller: NAT Semi DP8390BN Ethernet Controller
Ethernet Controller: NAT Semi DP8390BN Ethernet Controller
Etherlink II Rev C
Gate Array: 3588-02
Ethernet Controller: NAT Semi DP83901AV Ethernet Controller
Ethernet Controller: NAT Semi DP83901AV Ethernet Controller
Etherlink II Rev K
Gate Array: 3588-02
Ethernet Controller: NAT Semi DP8390BN Ethernet Controller
Ethernet Controller: NAT Semi DP8390BN Ethernet Controller
Etherlink II 16 (3C503-16)
Gate Array: 3588-03
Ethernet Controller: NAT Semi DP83901AV Ethernet Controller
Now people my age at least, all had the ultra ubiqutious:
Etherlink III (3C509)
Controller: 14-01303????
Ultra integrated almost single chip solution, - everything has been put into the custom chip that says as many will remember.. "Parallel Tasking". It's another AT&T made chip. So presumably this is the gate array, and all the glue logic and the Ethernet controller (don't know which one..) all bundled onto one IC.
Etherlink III EISA (3C579)
Controller; AT&T made 8350-03
Etherlink III EISA (3C592)
Controller; AT&T made "Parallel Tasking" chip 40-02032??
Tokenlink
Wow! Complicated beast this, looks like it would have been pricey too!
Controller: Texas Instrument TMS38030 System Interface Chip?
Quite a different beast this one (to be expected, as its Token Ring). Based on a Texas Instruments chip set. There is a TMS38030 controller, a TMS38010 Communications Processor, a TMS38021 Protocol Handler chip, TMS38051 and TMS38052 Ring interface pair, and what look to be two TI gate arrays, stamped with "LBASIC" and "PCASIC", and both are stamped 3COM also.
3C905 PCI (10/100Mbit)
Moved onto the "Parallel Tasking II 'Performance'" chip now. Fast Ethernet.