Fuse
There is a new spectrum emulator, ZXSP, looks quite tasty
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For your dashboard, there is one too. Ideal for a quick game, e.g. of Cracker, the Eurogamer christmas gift i mentioned, you can find the widget here
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There is a great new way to play old speccy games on your Mac. MySpeccy adds an online dimension, with global leaderboards and stuff. It is almost Xbox live. It works with Java emulation, but really speedy.
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My profile page: Romanista
The predecessor of the Spectrum, the ZX81 can be emulated using Mess
For those of you with a DS, and a flashcard, don't for get the great SpeccyDS