Astrocade emulation works well (though there are some missing sounds). If you plan to use one of the BASIC cartridges, then it can be tedious, but it does work. While there is emulation of the Knob, games that don't require work easiest.

Cart ROMs Astrocade Cartridge ROM images.
Hardware Emulation Hardware Emulation using FPGA.
M.E.S.S. Software Emulation using MESS. (Multiple Emulator Super System) - Download a version for Windows, DOS or MAC OS.