And here's one in that very issue of Sinclair User by the blog's favourite-gamer-artist-who-isn't-Russ-Nicholson, Gary Chalk (Lone Wolf/Red Wall/Talisman etc.) that I didn't know existed until yesterday when I found it looking for something entirely different and now totally forgotten.
Assault of the Ogroids is a strange mix of boardgame and random encounter table-driven sandbox. As can be seen if you read the scans (SUBTLE HINT), the idea is to pick a route across a gridded map and reach the other city in the 30 hours time limit. Each square has a terrain type which is keyed to a random encounter table, some of the entries of which are themselves keyed to random encounter subtables which should be manna from heaven for OSR sandbox haven't-a-fucking-clue-what-is-going-on-in-my-own-campaign enthusiasts (SUBTLE HINT).
There is a computer-moderated element to this, but you don't need an 1982 vintage home computer in order to play it - all it does is book-keep and generate d% and d8 results for you. It's going to be less hassle to just do it yourself with paper and dice.
Yes children, once upon a time we actually had to type in the source code ourselves if we wanted to run the thing. And then debug our typing errors. And then debug the typesetters typing errors. And then debug the coders errors. Upon such things men were built.
A couple of simple mechanics might arouse the interest of OSR sandboxers. Firstly, each terrain type has a time cost to cross it, meaning that the player has to balance crossing mountains with going around them and decide which is quickest. Secondly, the players stats detoriate with each square crossed with hard, fatiguing terrain costing more. Thirdly, you can run from any encounter but then you will "scatter" from the space which may put you in harder, slower terrain you didn't want to be in.
P.S. Any game in which your character token is represented as a man running away frit is Old School in my book.
(*) Sinclair User started off as a hobbyist magazine for early ZX81/Spectrum adopters but went downhill when the audience changed to a younger, games playing demographic.
(**) Maybe C64 magazines as well but who gives a fuck? Amstrad? Did they make computers?
(Scans from worldofspectrum.org)