nocash Atari 2600 emulator by martin korth

Emulation works with all games known to me. Precise timing emulation synchronizes CPU with the cathode ray beam. Auto-detects pal/ntsc frame rates & cartridge memory banking types. Emulates joysticks, paddles, keypads, and steering controller.
Debugger with breakpoints, symbolic debug info (labels), automatic I/O disassembler comments, built-in assembler/disassembler supports native/nocash syntaxes, upload to real atari function, help text includes full atari programming specs.

no$2k6 v1.1 Windows 32bit version (ca. 140 Kbytes, October 2012)
Older downloads:
no$2k6 v1.0 DOS version XT/AT compatible (ca. 100 Kbytes, July 2005)
no$2k6 v1.0 DOS version 80486 and worse (ca. 100 Kbytes, July 2005)
no$2k6 v1.0 Windows 32bit version (ca. 130 Kbytes, July 2005)

release notes

Programming Specs
2k6specs.htm atari 2600 programming specs, HTML version
2k6specs.txt atari 2600 programming specs, TXT version
atari 2600 schematic originally drawn by Jerzy Sobola (with some additions by myself)

Homebrew Games
Magic Floor - a search game (with sample source code for the no$2k6 assembler) - webpage for homebrew games (nice idea, but doesn't work on any of my browsers)
And, don't miss Oystron and Thrust - the best homebrew games I've ever seen.

AtariAge - nice webpage with games, schematics, faq (unfortunately all ultra-bloated html)

nocash homepage

According to the specs, it can make sounds like a "flute", a "rocket motor", and an "explosion".