The Blackjack game was more of a study (there must be lots of blackjack games for the ZX81, after all). That was my first attempt to write for the ZX81. My goal was to experiment the limits of the Sinclair BASIC, speed it up with some assembly and specially learn in the process. As the shuffling routine wouldn't run reasonably fast in BASIC even in the fast mode, I implemented the "Knuth Shuffle" algorithm in assembly. I also wrote some other routines in assembly to give the game more fluidity and a better presentation. In the end of the day I'm happy with the result (which is: "I learned quite a bit"). I hope next time I come up with something a little more original.
As for the "Raining Code", that's a port of the program I wrote for the MSX last year (https://www.youtube.com/watch?v=Xo0dbCHq7Rg).
Well, that's what I wanted to share and I hope you enjoy the programs. They both can be download from my blog: https://dimcavesoft.blogspot.com
P.S.: Blackjack requires 8kB and the Raining Code only 2kB.