Looks like XDA has done it again. The ancient (by tech standards) Nexus One has gotten a Jelly Bean port! It’s being called an alpha build, but it seems to be quite stable. The only things that may be problems are browser rendering issues (fixed by using Chrome) and possible broken tethering (unconfirmed). As you can see, the phone performs admirably (a little laggy, but this is expected for such an old device) and even Google Now is working.
However, you should be twice as cautious as usual. First of all, flashing of course always carries a risk and DroidDog nor developers are responsible for any possible damage. Second of all, you’d have to flash a new Jelly Bean hboot before flashing the ROM, which is even more dangerous. For those of you new to Android, I wouldn’t suggest flashing hboot. But if you do, enjoy! Hit the XDA source link for the thread to the ROM.