The emulator needs a kickstart system ROM file. Please drag the missing file into the empty chip socket. Or just touch or click the sockets.

most settings are permanent and will be saved to your local browser storage

kickstart roms ...df0dh0cut out sprite layers (stencil)cut out playfield layers (stencil)
game controller type settings
touch screen settings for virtual keyboard

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This is the place where you can create app or game specific customized overlay buttons with free positioning ...
app scope
compose an action sequence, for example

• loop5{j2fire1=>120ms=>j2fire0=>90ms} which will shoot 5 times
• or a literal action enclosed in single quotes e.g.'load"$",8'
• or key combos e.g. CTRL+W  pressControlLeft=>W=>releaseControlLeft
• or A=>await_action_button_released=>B
for A on button down and B on button up in locked mode (see settings)
• for more complex tasks you can also choose to add a javascript ...

... after created you can change the position of the action button by dragging ... when clicking the action button with a long press it goes into edit mode which takes you right back to here ...