Tape drives

Supported:

SCSI tape drives - Virtually all drives should work. (Send mail if you know of any incompatible drives.)
QIC-02 drives
QIC-117, QIC-40/80, QIC-3010/3020 (QIC-WIDE) drives
Most tape drives using the floppy controller should work. Various dedicated controllers (Colorado FC-10/FC-20, Mountain Mach-2, Iomega Tape Controller II) are also supported.

Unsupported:

Emerald and Tecmar QIC-02 tape controller cards
Drives that connect to the parallel port (eg: Colorado Trakker)
Some high speed tape controllers (Colorado TC-15)
Irwin AX250L/Accutrak 250 (not QIC-80)
IBM Internal Tape Backup Unit (not QIC-80)
COREtape Light

Mice

Supported:

Microsoft serial mouse
Mouse Systems serial mouse
Logitech Mouseman serial mouse
Logitech serial mouse
ATI XL Inport busmouse
C&T 82C710 (QuickPort) (Toshiba, TI Travelmate)
Microsoft busmouse
Logitech busmouse
PS/2 (auxiliary device) mouse

Computers/Motherboards/BIOS

ISA, VLB, EISA, and PCI buses are all supported.

PS/2 and Microchannel (MCA) is not supported.

Controllers (I/O)

Any standard serial/parallel/joystick/combo cards. Linux supports 8250, 16450, 16550, and 16550A UART's. Cards that support non-standard IRQ's (IRQ > 9) can be used.

Controllers (multiport)

Non-intelligent cards

Supported:

AST FourPort and clones (4 port)
Accent Async-4 (4 port)
Arnet Multiport-8 (8 port)
Bell Technologies HUB6 (6 port)
Boca BB-1004, 1008 (4, 8 port) - no DTR, DSR, and CD
Boca BB-2016 (16 port)
Boca IO/AT66 (6 port)
Boca IO 2by4 (4 serial / 2 parallel, uses 5 IRQ's)
Computone ValuePort (4, 6, 8 port) (AST FourPort compatible)
DigiBoard PC/X (4, 8, 16 port)
Comtrol Hostess 550 (4, 8 port)
PC-COMM 4-port (4 port)
SIIG I/O Expander 4S (4 port, uses 4 IRQ's)
STB 4-COM (4 port)
Twincom ACI/550
Usenet Serial Board II (4 port)

Intelligent cards

Supported:

Cyclades Cyclom-8Y/16Y (8, 16 port) (ISA/PCI)
Stallion EasyIO (ISA) / EasyConnection 8/32 (ISA/MCA)
Stallion EasyConnection 8/64 / ONboard (ISA/EISA/MCA) / Brumby / Stallion (ISA)

Others:

Comtrol RocketPort (8/16/32 port)
Computone IntelliPort II (4/8/16 port)
DigiBoard COM/Xi
DigiBoard PC/Xe (ISA) and PC/Xi (EISA)
Hayes ESP8
Moxa C218 (8 port) / C320 (8/16/24/32 expandable)
Specialix SIO/XIO (modular, 4 to 32 ports)

PCMCIA Cards

Virtually all Modem, SCSI and ethernet cards are supported