What console/handheld platform libraries can you play using the hardware that you currently own? Obviously not taking piracy or illegal emulation into account. Based on the consoles you own and their backwards compatibility, what games can you play.

I own PS5, PS4, PS3, PS Vita, Switch, 3DS, and Wii.

Through PS5 I can play - PS5 + PS4 games.

Through PS4 I can play - PS4 games.

Through PS3 (Original Fat 60GB) I can play - PS3, most PS2, and PS1 games.

Through PS Vita I can play - Vita games, PSP digital games.

Through Switch I can play - Switch games.

Through 3DS I can play - 3DS + DS games.

Through Wii I can play - Wii + Gamecube games.

So even though I own 7 pieces of gaming hardware, I can access the libraries of 12 different platforms thanks to BC. I do play across libraries pretty regularly actually.

What about you?

Here's an interesting thought experiment, what's the minimum amount of hardware you would need to own to be able to access the libraries of all mainstream gaming platforms?

Gameboy games, original, color and advance on my GBA.
DS on my DS lite.
3DS games on my 3DS.
PS1 and PS3 games on my PS3.
(most) PS4 and PS5 Games on my PS5.
Gamecube games on my gamecube.
Switch games on my switch (as well as many retro games of note on Nintendo Online)

11 libraries on 7 systems.
I could get rid of my two DS lites and still access the same libraries. But I like using it more than the 3DS.
All games I care about on Snes and Nes are present on the switch, so even if I do not have access to the full libraries of the consoles I can play the games I like from those consoles.

Only thing I miss that I would like is a Wii for the Wii games. Had one but my ex got to keep that when we split. Used mostly for Gamecube games anyway but miss Mario Galaxy 2 and RE4 Wii-edition.
Had a PS2 and a WiiU in the past but all games I liked from them can be played on newer hardware because of rereleases or upgrades.

The ultimate combo (imo)
GBA for all the gameboy line games.
(new)3DS for all the DS-line games
Wii for Wii and Gamecube games
Fat PS3 for PS1,PS2 and PS3 games
PS5 for PS4 and PS5 games
XboX series X for most of the total Xbox library
Switch for Switch games and anything of note from WiiU era + a lot of classics from retro systems.
7 systems, 17 libraries

Nintendo

NES

SNES/SFC

N64

Gamecube

Wii

Wii U

Switch

Game Boy

GBC

GBA

GBA Player

DS

3DS

SEGA

Master System

Genesis/Mega Drive

Genesis Mini 2

SEGA CD

32X

Saturn

JP Saturn

JP Dreamcast

 Dreamcast

Dreameye

Game Gear

NEC

TurboGrafX 16

TUbo CD

PCE/TG16 Mini

Xbox

Xbox

Xbox 360

*GP games so whatever XBO and SX games are on PC and when Sub is Active

Steam/GOG

Sony

PS1

JP PS1

PSone

PS2

PS3 SS

PS4

PS5

PocketStation

PSP 3000

PSVita 1000

I want Neo Geo systems and arcade systems but just too pricey.

NES
SNES
Genesis - (+Master System)
N64
Dreamcast
GBA - (+GB)
DS - (+GBA)
Gamecube - (+GBA)
Wii - (+GC)
WiiU - (+Wii)
PS3 - (+PS1)
PS4
3DS - (+DS)
Switch

14 systems, access to 17 different libraries (not counting Switch Online, Virtual Console, etc). Lists like these always remind me of how stupid I was for selling my TurboGrafx-16. :/

Game Boy Advance: BGA, GBC, GB games, additionally some extra content with the Gamecube.
SNES: SNES
NES: NES
Megadrive: Megadrive
N64: N64
PS2: PS1, PS2
Gamecube: Gamecube
Wii: Gamecube, Wii
Wii U: Wii, Wii U
Switch: Switch
DS Lite: GBA, DS

NES (got a Famiclone and a NES Mini)
SNES (partialy and limited, SNES Mini)
N64 (Pikachu Edition)
Game Boy Family (got two GBA SPs)
NDS (DS Lite)
3DS (One New 3DS, one New 2DS XL)
Gamecube
Wii+Wii U (got a Wii U)
Switch
PS1 + PS2 (got a PS2)
PS3
PS4
PSP
PSVita

I have access to Switch, PS4. Wii U/Wii, Gamecube, GBA, N64, SNES, NES, PS3/PS1.

Switch and PS4 have pretty much every game on them that I cared about from the Wii/PS3/Xbox 360 era, so there's also that;

Through Switch, I have access to a plethora of games across the entire spectrum of the industry starting from Pong on Atari 50.

I own an Atari 2600, NES, Genesis, Gameboy, SNES, Sega CD, PS1, N64, Dreamcast, PS2, GBA, Gamecube, DS, Xbox 360, PS4, Xbox One, Switch and PS5. I use to own a Saturn, an original Xbox, a PS3 and a PSP as well, but a former GF sold off all my stuff without my permission, and I still haven't gotten to these things yet. The Saturn hurts the most, since I had a whole slew of (now) very rare and expensive games. Who knows when I'll be able to buy them again.

But as far as access to game libraries, if you add the above to digital access... pretty much every major library ever.

Switch, PS5, PC, so yeah, these three plus the PS4 through BC. Also, there's a PS2 in a box somewhere around the house, might include it and the PS1 too in that case.

But... you can legally emulate most Nintendo consoles (NES/SNES/N64/GC/Wii/GB/GBA/DS) and everything else 4th gen and earlier on a PC without even owning them since they don't require a dumped BIOS. So that's a lot of possibilities right there.