Having only ever played modded, vanilla engineering like this just absolutely floors me.
RP2 logic gates are all doable in vanilla. It just makes it easier to screw around with redstone without having to look at the wiki every 4 seconds to look at the next step.
Etho has some machines that do exactly what some of the modded blocks do, and sometimes his massive machines do it better than the mods do.
Frames are also the same thing as the gates, pistons allow for a system of movement of players and blocks, although it's artificial and not true independant movement.
With the new 1.5 hopper functionalities, most of RP2's item transport systems will be doable in vanilla. You could always use pistons to move items, but you couldn't put them into a furnace or a chest. There are vanilla machines that allow items to travel upwards utilizing water, so that's possible aswell.
The list goes on and on. You would be surprised at how many modded things aren't actually needed because they're possible to do in vanilla. Gravisuite? Piston elevator ****
. Yeah, I can't move while doing it, and I can sometimes suffocate and die in the ceiling, and one piece of redstone out of place would break the machine, but who cares?
Keep in mind redstone can also replace
some aspects of computercraft, although not all. I've never used computercraft in any builds because I can simply do what the computer/turtle can do but with redstone.