a2, an Apple II emulator in C, by Rich Skrenta and Tom Markson. Designed to be as fast as possible. Does not support graphics.
ApplePC v2.52beta, by David Ellsworth, an Apple ][+, //e, and //c emulator for DOS, based on Randy Spurlock's Apl2Emu version 1. Includes boot disks for Apple II DOS 3.3 and ProDOS.
AppleWin Version 1.10, by Michael O'Brien an Apple //e Emulator for Windows 95 and NT, also runs under Windows 3.1 with the Win32s extensions.
Source code for AppleWin Version 1.10.
A program by Andy McFadden that converts files with Apple II ProDOS mapping (e.g. the output of NuLib, see below) to Apple II DOS 3.3 mapping (e.g. for use with ApplePC, see above) and vice versa. DOS executable and C source code.
NuLib v3.24 (January 1993), an archiver for NuFX (Apple II ShrinkIt) files, by Andy McFadden. DOS executable and documentation. (C source code is in download-tools/pc/nulibsrc.zip)