The HBAs Linus uses in his new storinators are HighPoint Rocket 750s (if I remember correctly), he has two in each new storinator.
One of the ports on this card supports 4 SAS or SATA drives (there are either backplanes which do the "splitting" or you can get cables that split into 4 SATA-Connectors).
In general those cards are either called HBA (host bus adapter) which basically pass-though each individual drive to the OS, or RAID cards, which create RAID-arrays over multiple drives and present it to the OS as one big drive.
