Im really happy with all the devices included with Renoise (ringmod, hydra, LFO, Signal Folower, etc). They are very useful, and not fancy additions that bloated the software. But a Frequency shifter is really needed, it is a basic and classic device for Electronic Music creation.
I wouldn’t call it exactly “basic and classic device”. More like a niche effect not even known by many electronic musicians.
Are you sure you don’t mean pitch shifter?
Anyway, I’m definitely not against this 
Pitch and frequency are very closely related. English isn’t everybody’s first language.
+1 to a pitch shifter!
+1 for both frequency shifter and pitch shifter
Edit: I mistakenly thought capitan_mission was talking about a totally different feature!
Saying that a pitch/frequency shifter is “really needed” is a matter of personal opinion, so I can’t argue too much about that. What I can say, however, is that a pitch shifter is definitely not a “basic” device, and is definitely not a basic thing to program, either.
Pitch shifters (and time stretchers) are fairly specialised things which can be technically very difficult to create, and often take many months (or even years) of research and development, not to mention the countless hours of fine-tuning and tweaking algorithms to actually make them sound good and be musically useful, rather than just being good from a technical point of view.
That’s why a lot of the existing software you find usually either sounds like crap, or only sounds good after a lot of CPU intensive offline processing, and why pretty much all of the advanced libraries/engines that actually sound good (whether they work in realtime or not) cost a lot of money to license commercially, because the programmers have dedicated years of their life to improving their algorithms.
The Renoise team is still quite small and has more important features to focus on, so we can’t expect them to suddenly dedicate their time to creating an amazing new pitch/time library. The reality is that they’d probably have to use an existing library such as Rubber Band, DIRAC, SoundTouch, etc. Taking advantage of such a 3rd party library would probably force up the price of Renoise in order to cover the licensing fees.
Anyway… All I’m trying to say is that this topic is a bit more complicated than most people assume.
By Basic Device I thing he was referring to it as something that is missing that can be found on many multi-effects units dating back for the last twenty (possibly thirty) odd years. The kind of realm where you know you are using it as an Effect, not for high quality Pitch Correction/Time Stretching. Although that would obviously be very nice!
Hmmm… capitan_mission: sorry if there’s been any confusion here on my part. Perhaps you could give some examples (video ideally, or mp3, etc) of what type of effect you’re talking about exactly. I assumed that you were talking about a high quality method for pitch/frequency adjustment.
I call it “frequency” and not “pitch” because is a more open term. “Pitch represents the perceived fundamental frequency of a sound”.
I call it a classic device because these techniques were used in the times of Stockhausen and even before.
I dont know how difficult it would be for the Renoise developers, but I’m not talking about a time stretching thing… The ringmod changes the frequency, but it makes a multiplication of 2 signals.
+1 for lofi pitch shifter. Maybe simple granular approach would be most flexible. And when that is done a higher-end code could use the same interface/fx commands if such is licensed from somewhere. I like native effects.
I’ve been checking out a couple of videos on YouTube…
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This is more like what you had in mind I guess?
Yeah : )
In the software world, the device in Ableton Live has the option to choose between frequency shifter-ring mod, amount, rate, phase, wave shape & dry/wet options.
Formant filter please! 
Apologies for the misunderstanding!
I think it will still be a bit tricky to create a really nice frequency shifter, especially if you want a very accurate emulation of that lovely classic analogue sound/feeling, since even the simplest analogue circuits can cause the most insane programming headaches when trying to recreate them in digital form. Nevertheless, it probably wouldn’t be quite the huge pain in the ass I thought we were talking about earlier. 
No problem, man! : )
I hope it wouldn’t be a big problem, is not easy to get that amazing analog sound, but we can try!
frq.shifter +1
The thing about the frequency shifter is that you can get some wicked effects by mixing dry/wet signals with al low frequency shift applied .
A very good commercial freq.shifter is ohm force hematohm .
A freq.shifter has more in common with a ring mod than with a pitch shifter .where aring mod modulates the amplitude of the signal , when the mod rate is in the khz range ; you gets lots of sidebands and added harmonics , same thing goes with freq. shifter .
I am not sure if this will help, however, since you specifically said frequency shifter and I have happened to use one, i can refer you to a good free one.
It is not the same as a pitch shifter as it does not maintain harmonic relationships.
Hope this helps! 
The freq shifter I use regularly (not pitch shifter) is Ohmboyz Hematohm: http://www.youtube.com/watch?v=oDGJvNHZfow
Not free though.
the discussions about it being native aside; you can use sampletank (which is free nowadays) to do both regular pitching and pitching with rhythm intact. also, with pitch intact and rhythm changed. two different algorithms included which have different characteristics.
amazing plug-in(s). waw… 
thanks.