"Alejandro Jodorowsky's Dune: an Exhibition of a Film of a Book that Never Was" has just opened at the Drawing Room Gallery  in east London (ends 25 October). Taking the cult Chilean film-maker 's unsuccessful 1976 attempt at an adaptation of Frank Herbert's science-fiction novel as its departure point, the show assembles apocalyptic works by the likes of Vidya Gastaldon and Matthew Day Jackson to explore what the curator calls "a parallel cinematic world".
Jodorowsky's Dune has a decent claim to being the greatest film never made. That it aimed to pool the talents of Pink Floyd, Orson Welles, Mick Jagger and visual artists including H R Geiger (who later worked on Ridley Scott's Alien), Moebius and Chris Foss would be good enough. That Jodorowsky wanted to cast Salvador Dalí as "Emperor of the Universe", only for Dalí to insist on being paid $100,000 an hour so that he could "earn more than Greta Garbo", tips the balance even further in its favour.
But what about Tarkovsky's never-started film of Hamlet? Or Darren Aronofsky's proposed take  on Batman? Or Nick Cave's time-travelling Gladiator sequel ? Feel free to suggest your own additions to the canon in the comment box below.
Then take a look at Toby Litt's encomium  on science fiction from this week's issue.