z81 - A freeware ZX80/81 emulator for Linux/i386. - http://rus.members.beeb.net/z81.html
Z80Stealth - A freeware ZX80 emulator for DOS which draws the screen lines by lint, thus fixing some flicker problems seen in other emulators. - http://z80stealth.emuunlim.com/
VB81 - Sinclair ZX81 emulator written in VisualBasic. Runs under Windows on a 133MHz Pentium or better. Includes source. - http://freestuff.grok.co.uk/vb81/
NO$ZX81 - A freeware ZX80/81 emulator for DOS and Windows. - http://www.work.de/nocash/zx8.htm