All credit goes to Wedge666 (thread here), to posters in his thread for customisation and of course to first Action Screen developper (I would quote him if I knew. Anyone knows? Or was it adapted from a HTC application?).
As in the original from Wedge666, you trigger with Manila Home tab right soft key, and you can configure program to make it running in background if you wish (quicker?). You have no confirmation message on shut down or reset.
You get advice about installation and basic customisation explanation in the HD thread.
EDIT : on Roms with Action Screen already installed, it may be difficult to completely uninstall this version. And you need to apply the fix here.