If you're looking for an Atari 2600 emulator, look no further than Stella. The latest stable version, 4.0, of Stella has been posted. Here is the changelog:
* Ported Stella to SDL2, which brings many new features. Among the largest improvements is native hardware acceleration support for Windows (Direct3D) and Linux/OSX (OpenGL). It is also now possible to port Stella to iOS and Android devices using OpenGLES. Hardware acceleration is now required, which means up-to-date drivers are needed. Software rendering is still present, but is somewhat unoptimized and unsupported going forward.
* Fullscreen video modes now use the desktop resolution. Switching to fullscreen and back to windowed mode no longer rearranges icons on your desktop.
* TIA TV effects are now available in all video modes, since hardware acceleration is a requirement.
* Added a much more detailed view of cart extended RAM to a new debugger tab. Special thanks to SpiceWare for this implementation.
* Added preliminary support for 'DASH' bankswitching scheme by A. Davie.
* The AtariVox and SaveKey controllers now have the ability in the debugger to completely erase the virtual EEPROM data.
* Added 'savesnap' debugger prompt command, and also associated context menu item to the debugger TIA output area. This saves the current TIA image to a PNG file.
* Added 'hidecursor' commandline option, which allows to completely disable showing the mouse cursor (useful on systems that don't have a mouse).
* Removed 'uipalette' option, as the original palette is no longer supported.
* Updated included PNG library to latest stable version.
You can download Stella here: http://stella.sourceforge.net/