My very first published code was a machine code hack that added the iconic heartbeat sounds to the Apple Invaders game, published in the letters page of Practical Computing back in March 1982. I was 15 years old and already on my second home computer by then, as my dad had bought me a TRS-80 back in 1981 and then I sold it and bought an Apple II. A little later, I developed commercial software across the Atari 800, Commodore 64, Sinclair QL, and Atari ST. My work ranged from games to utilities and creative tools. My parents helped run the "business", such that it was, and I just came up with the ideas and did the programming in our front room. These are the highlights...
Early 8-bit title inspired by my favourite arcade game - Rally-X. It taught me to work close to the hardware and budget every byte and cycle.
Used the C64's SID and sprite system to deliver a nice Atic Atac style maze explorer game. Despite a good try at marketing by the publishers, it didn't sell all that well, but it got some nice reviews and some not so nice.
My first foray into 16-bit computing and where I learned to code in C. This was a spell-checker supporting the QL's word processor. I couldn't believe it didn't have a spell-checker, so decided to add one!
Graphical interface, later with mouse support - an effort to make the QL more approachable and modern. It was no Microsoft Windows, but not bad for 1985. The real challenge was trying to write a complete GUI in 68000 machine code that fitted on just a 16 kb EPROM! Yes, just 16 kilobytes. I try telling students that today and they just don't believe me.
A paint and graphics program built for the ST's higher resolution display and GEM environment. Its main claim to fame was finding a way to get thousands of colours onto the screen at once to try to match the Amiga.
Along the way, I contributed code to other programs like sound effects for Eidersoft's ST Karate (developed by some nice ex-Psion programmers who later formed the Bitmap Brothers) and implemented copy protection for that and several other titles. It all feels like a distant dream now, but those 8-bit and early 16-bit days were really a lot of fun. If you have any questions about licensing for these old titles, then sorry, I can't help, as I have no idea who still owns them.