You may be aware that I've been working with Tony Thompson to produce a PC editor for my Spectrum Arcade Game Designer. The good news is that the Spectrum version is working and should be released before too long.
Going further, we'd like this tool to be capable of producing games for a variety of 8-bit platforms so as part of this, I'm presently converting Arcade Game Designer to the Amstrad CPC464 so that it can ultimately become part of the PC editor as well.
At some point in the near future I'll be releasing a work-in-progress demo of the Amstrad tool, probably as a snapshot. There's a topic dedicated to the Amstrad version over at the AGD forums, so keep checking back there for further updates.
Further versions are planned - an Acorn Atom port is in the pipeline courtesy of Kees van Oss and I'm hoping to find further volunteers to convert AGD to other machines such as the BBC, C64, Dragon, Oric...