Ports of Entry: Magnetic Fields

Unknown lead platform:

 

Pacmania

Released for Commodore 64 and VIC-20 in 1983

Because the VIC-20 version is credited to Ian Creasey and not lead programmer Shaun Southern, I think it likely the VIC-20 is a port of Southern's C64 design.

 

Trailblazer

Released for Commodore 64 and Commodore 16 in 1986

Ported to Amstrad CPC, Atari 8-bit, Atari ST, MSX, & ZX Spectrum in 1986

 

Super Cars

Released for Amiga, Amstrad CPC, and Atari ST in 1990.

Ported to ZX Spectrum in 1990.

Amiga supports 48 colors ingame (split 32/16 between gameplay and status bar) and Atari ST only 32 (split 16/16), suggesting to me an Amiga original design..

 

Lotus Esprit Turbo Challenge

Released for Amiga, Amstrad CPC, Atari ST, Commodore 64, & ZX Spectrum in 1990

Amstrad CPC and ZX Spectrum are credited to Ali Davidson rather than Shaun Southern.

Once again, Amiga supports 48 colors ingame (32 on the top splitscreen, 16 on the bottom), while Atari ST only supports 32 (16 per splitscreen).

 

Lotus Turbo Challenge 2

Released for Amiga & Atari ST in 1991

Ported to Acorn & Genesis in 1992

This time, likely due to the full frame viewport, Amiga has only 32 colors ingame, while Atari ST is 16.

 

Lotus III: The Ultimate Challenge

Released for Amiga & Atari ST in 1992

Ported to Genesis & PC in 1993

Amiga still supports 32 colors ingame. Atari ST does up to 20 through what I must assume are some scanline shenanigans.

Select chronology: 

 

 

Title	Lead platform	Date	Contemporary ports
Pacmania	???	1983	Same-year releases on C64 & VIC-20
Kikstart: Off-Road Simulator	Commodore 64	1985
Trailblazer	???	1986	Same-year releases on C64 & Commodore 16 Same-year ports to various microcomputers
Super Cars	???	1990	Same-year releases on Amiga, Amstrad CPC, & Atari ST Same-year port to ZX Spectrum
Lotus Esprit Turbo Challenge	???	1990	Too many to fit here
Lotus Turbo Challenge 2	???	1991	Same-year releases on Amiga & Atari ST 1992 ports to Acorn & Genesis
Lotus III: The Ultimate Challenge	???	1992	Same-year releases on Amiga & Atari ST 1993 ports to Genesis & PC
Network Q RAC Rally Championship	DOS	1996
Mobil 1 Rally Championship	Windows	11/19/1999	2000 port to PS1 by HotGen Studios