This is not a new emulator but is rather an old VIC 20 emulator (V20 1.3) running in another much newer PC emulator (jdosbox). I couldn't resist trying this. Although slow, I'm quite surprised that it isn't slower. Give it a go to see what you think.
Click on the applet to activate key capture and from there you should be away and running.
ESC brings up the menu for loading cartridges, tapes and snapshots. When you choose a cartridge file, it is usually sufficient to simply hit ENTER a few times to accept all the default loading options.
The joystick is emulated with the numeric keypad. The 0/Ins key is the fire button.