This amazing demo was created for the ZX81 and shown exclusively at the Retro Computer Museum Valentine's Event 2015 at Snibston Discovery Centre in Leicester. It's incredible to see a game such as this on an 1 kB-16kb memory system so hopefully we see a release this year!
http://www.indieretronews.com/2015/02/dragons-lair-appears-on-sinclair-zx81.html