Well, my post on the ultimate pimped-out ZX81 drew a lot of attention; mostly centred around the mystery expansion board that was included in the myriad of components of which this behemoth was comprised. A closer picture shows it to be some kind of EPROM from ‘Orme Electronics’.
But what does it do? Well, the best clues can be found from the wonderful ZX81 Stuff resource. Sadly, I can’t find any photographs to confirm but it looks to me to be the first item in their Orme list. It can’t be an EPROM programmer as the chip is soldered in and there would be no practical way of removing it if it wasn’t. Without instructions I’m still a bit lost but I’m going with an EPROM programmed with Breakout, Life and a Toolkit of some description.