See http://www.worldofspectrum.org/ for information about the ZX Spectrum, its emulators, snapshots, and tools.
JPP version 1.0, by Arnt Gulbrandsen. Emulates a Sinclair Spectrum 48k Z80-based computer on any PC with at least a 386 processor and VGA graphics. 14 games included.
Mac Spectacle, a ZX Spectrum emulator for the Macintosh, version 1.5.5, by Guenter Woigk. Needs System 7, an 68020+ or PowerPC, Color QuickDraw, and QuickTime.
Spectrum Emulator Snapshot File Converter version 1.10, originally by Henk de Groot, this version by Damien Burke, converts between the snapshot formats of different emulators
UnQuill v0.12.0, by John Elliott. Reads a snapshot (Spectrum, Commodore and CPC formats are supported) of an adventure game written with the Quill, and can:
[file is linked from programming/quill/unquill.zip]
Sinclair ZX Spectrum Emulator by Gerton A. Lunter, shareware version 3.05 (11nov96). Emulates ZX Spectrum 48k model 2 or 3 and Spectrum 128k on any PC with 640k base memory or EMS.