left to right, had to search a few of them. You're probably not out of it, it's just relatively niche professional stuff. Half of them are only relevant for media professionals for example.

Sonnet card - adds storage via a couple SATA SSDs

OWC 8M2 - adds storage via up to 8 NVME drives

Avid HDX card, runs DSP for ProTools (audio)

Kona 5, video capture and I/O

Lynx E44, high-quality audio I/O

Blackmagic decklink SDI 4k - SDI video capture

ATTO high-speed ethernet card, maybe 50GbE

ATTO Celerity Fibre Channel Adapter - Storage HBA

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Expansion cards, they were supported by the original PC from the 80s and even before that.