...

Layer 1: General classification of systems

1. Europe/American Homecomputer like C64 / Amiga / Atari
2. asian Homecomputer like PC88 / PC98
3. Consoles like NES / Playstation / Xbox
4. Handhelds like Gameboy / Lynx / PSP
5. Mobiles / Mobile Operating System like iPhone / Palm / Windows Mobile
6. Tablets like iPad
7. Operating Systems like DOS / Windows / Linux
8. Arcade
9. cross-platform environments like Flash / HTML / Z-Code
10. DVD-Player-Games

Layer 1 of this list is finalized here!

Layer 2: concrete platform from every entry of level 1

...

1. 3DO
2. Apple Pippin
3. Atari 2600
4. Atari 5200
5. Atari 7800
6. Atari Jaguar
7. Atari Jaguar CD
8. Bally Astrocade
9. Casio PV-1000
10. Cassette Vision
11. CD-i
12. ColecoVision
13. Creativision
14. Dreamcast
15. Emerson Arcadia
16. Fairchild Channel F
17. Famicom Disk System
18. GameCube

19. Interton VC4000

20. Intellivision
21. Magnavox Odyssey
22. Master System
23. Mega CD
24. Mega Drive
25. Neo Geo AES
26. Neo Geo CD
27. Nintendo 64
28. Nintendo 64DD
29. Nintendo Entertainment System
30. PC-FX
31. Phillips G7000 (Odyssey²)
32. Phillips G7400 (Odyssey³)
33. Playstation 1
34. Playstation 2
35. Playstation 3
36. Playstation 4
37. RCA Studio II
38. Sega SG-1000
39. Sega 32X
40. Sega Pico
41. Sega Saturn 
42. Super A' can
43. Super Cassette Vision
44. Super Grafx
45. Super Nintendo Entertainment System
46. Turbografx-16 (PC Engine)
47. Turbografx-CD
48. Vectrex
49. Virtual Boy
50. Wii
51. Wii U
52. Xbox
53. Xbox 360
54. Xbox One

Layer 1.4: Handhelds like Gameboy / Lynx / PSP

...