Just an idea I have for a topic.

What are the best, your favorite, or most interesting cards for a computer that you are aware of? They can be sound cards, video capture cards, cards that add USB ports, pretty much anything that goes in/attached to a computer and that would be considered a card, with the exception of video cards that contain GPUs. (Video card discussions are extremely common, and that sort of discussion is not what I am interested in here.)

So, any thoughts?

Ph... never mind.

I have a Soundblaster Z, mostly for having EAX in older games and ASIO drivers. (And it sounds a bit better than the Realtek)
The old X-Fi music still worked, until my latest GPU got in the way of my one PCI slot...

The most 'exotic' cards I've encountered - according to fuzzy memory - are a RAM add-on card back in the early 90s, and the cards that handle motion control / interface duties on some of the industrial machines I work on.

Back in the early to mid 90s I worked at a company that manufactured PC telephony cards which were quite flexible. Not only could they be used as multi-user voicemail systems, they could work as autodialers and interfaces to command the host PC to carry out whatever action the user desired. There were even a couple of games which supported them as sound cards (Jonny Quest is one I remember). We had four separate products: a single port, two port and two four port cards. Our original four port card was an ambitious design based around a Xilinx gate array, but the prototypes suffered from some inherent design flaws so we were forced to scrap it and come up with a new design based around an 80186 CPU.

Another interesting device that I had was the Covox Voice Master Key. It was an external sound card with a speaker built into the top and whole unit was made out of metal (steel, I think). Mine got lost years ago in one of my many relocations.

Then there were "hard cards" which were internal expansion cards which contained a disk controller and hard drive in one. I never had one, but I always thought they were interesting.

I never owned a Mac, but I seem to remember something about an add-on card which actually had a 486 or possibly a Pentium on board which allowed the host Mac to run PC operating systems and software.

most interesting computer cards?
I was talking to one the other day and we had an indepth conversation about it's actual function ability and it told me that it was very excited about bringing exciting new colours into peoples lives:)

I think the story of the Hercules Graphics Card is a little fascinating. See, the IBM ASCII system was well accepted, but it couldn't address pixels directly. There was a Hindi engineer who wanted to use his native language, but the IBM PC and the then standard MDA cards of the time couldn't render the graphics which would be required.

I realize that's loopholing it a fair bit, as I can't exactly think of anything else.

I used to work at a factory. There we have an old computer running DOS. On the motherboard there is this giant card that uses 2 isa slots. The card will then be connected to a big machine via cable similar to TV cable. That big machine is a co2 based laser engraving machine, and that giant card is used to control the machine. All runs on ancient DOS operating system.

Not uncommon and not special, but I really love the original AdLib Music Synthesizer Card (1987).
However, the original one and its revision (1990) were not sold at my area.

So, my first 100% AdLib compatible sound card was a bootleg of the 1987 version.
For many retro gamers, MIDI music in games are their childhood memory.
For me, PC speaker and AdLib audio are my childhood memory.

The interesting part is here:
You can use a unofficial AdLib sound card on a parallel port:
https://www.raphnet.net/electronique/adlib/adlib_en.php
http://nerdlypleasures.blogspot.com/2017/12/parallel-serial-sound-card-emulation.html

The Creative Soundblaster 16 sound card I got for my 486 was glorious. I can't remember which the first game I played with it was, but I know the first game I wanted to play with it was Warcraft 2. Hearing that menu music coming from my own computer for the first time was one of the, if not the greatest gaming high I've ever experienced

You didn't specify PC, so for current tech, I'd add the Xena/Xorro stuff for the Amiga X5000.

For older stuff, the most interesting for me (and no-one else) would have to be the stereo recording/playback ISA card I made back in school (some 27 years ago) with a couple of Cypress CODECs and about 80 other ICs.

Even older, the Action Replay cartridge for the Commodore 64 was pretty nice.

Since this topic seems to be mostly talking about classic computer hardware, a tweet reminded me of something I've read about: The Applied Engineering PC Transporter.

This piece of hardware, if connected to an Apple 2 computer, would allow it to run software meant for PCs, in particular MS-DOS. Basically, it was an IBM compatible PC in the form of an expansion card for the Apple 2.

There's also the Bridgeboard, which was an add-on for the Amiga that would allow running PC software including MS-DOS.

Apparently, MAME has code to emulate the PC Transporter, but the source code is the only reference that I get from a source, so people haven't really talked about this capability. It might, as a history lesson, be interesting to try this.

Also, I stumbled across an article about this sort of thing from 1989:
https://www.atarimagazines.com/compute/issue106/coming_together.php
It seems rather quaint by today's standards, in particular the editorials about emulation, but it's worth it for those interested in compute history.

Here's a rather interesting quote from the article: Isn't it amazing how things have changed? (Yet there are some thing that stay the same.)

Might look at LGR's OddWare, which shows off interesting things, like a parallel port sound device.

I had a card that would allow me to interrupt any [Apple //e] program running. I forget what it was called, but it allowed one to, say, stop a game and take a screenshot (built-in feature), or, save the executable code in memory … for offline archival purposes, of course, for genuine licence holders to protect their investments. :D

Roland LAPC-I.

I think it was the longest ISA-card I ever had, extending to both edges of the standard PC case, so basically it was as long as any ISA card (or other type of card for that matter) could possibly be.

And oh boy, did it make PC games sound great, like a whole symphony orchestra inside your PC.

https://en.wikipedia.org/wiki/Roland_LAPC-I