A sword engine that's well presented and commented. If you really can't go through the bother of programming your own sword engine for a 1 char player MZX game, then it might be worth looking into this one. However, one look internally also shows that it's full of reused sword frame code and rel player commands. If you're looking for something elegantly coded or easily modifiable, this probably isn't your engine.

PS. What is it with 13 year olds and random homophobic comments in their game?