Jasper ZX Spectrum Emulator by Andrew Pollard and Adam Davidson

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 BASIC 

 EDIT               F1
 CAPS LOCK          F2
 LEFT               F5,SHIFT+LEFT
 DOWN               F6,SHIFT+DOWN
 UP                 F7,SHIFT+UP
 RIGHT              F8,SHIFT+RIGHT

 GRAPHICS MODE      F9
 E MODE             TAB
 CAPS SHIFT         CONTROL
 SYMBOL SHIFT       ALT,META

 PAUSE/LOAD URL     ESC,HOME
 RESET SPECTRUM     END

Utility3 Zeus Source Code

To list the source code from within the Zeus Z80 assembler, click on the screen and press the ENTER key.
To assemble press [F9] (twice) to clear the screen.
Then press A to assemble then X to execute.
Pressing Q will quit returning you to the assembler.
From within the disassembler -
Just enter hex digits to change address.
You won't, of course, be able to change ROMS.

You can see the full Zeus Instruction Manual here
The TASM source file is available for download together with the above Z80 emulator snapshot.