Yea, race cars with the SMG have "dog engagement" gears instead of synchros. They wear out fast, but allow almost instant gear changes when upshifting without even touching the clutch.

As for clutchless shifting on a standard, you have to match the RPMs EXACTLY or your synchro is going to hurt. If you grind, the mesh gear will strip and depending on wether they are made of plastic or titanium you may need to rebuild soon after.

Going out of gear, however, I have found myself pulling out of gear at the exact moment I let off the gas just before I hit the clutch. It's that brief moment where there is no load on the gearbox that you can do that. A blik of an eye sooner or faster and the mesh ring is not going to let it go out.

Just use the clutch, it's a faster way to change gear.

For decelerating, you can pull it out of gear at the exact moment the RPM falls just above idle. It's there that there is also no load on the gearbox. That saves you one clutch pushing or several clutchings while downshifting sequentially.