Soundforge is my editor of choice. When mixing, I never export a file directly from Sonar. I bounce to track, use the "Utilities" menu to load the bounce into Soundforge, check RMS levels, run a spectrum analysis, then save the file from there. That makes it a little easier to jump right back into the project and tweak as needed. Also, if I master something myself instead of shipping it off to our regular mastering house, I use Soundforge, since again, Sonar doesn't have native tools for offline RMS/spectral analysis.
 
Sure would be nice if Sonar had something like Soundforge's "Statistics" command....hint hint.... ;-) Y'know, select a track or clip, go to the Process menu, and be able to check that selection's RMS/peak/DC levels. That would be a massively useful tool, both for mastering purposes and tracking. Say you're trying to balance two guitar tracks: one with lots of low end but not much transient info, the other with lots of transients but very little energy below 150Hz. Being able to analyze their respective RMS levels in place would be really useful to confirm (or not) what your ears are telling you.

noynekker
Time stretch Render (I find Audio Snap mostly unusable)
 
Taming plosives and rogue peaks (faster than creating a bunch of tiny envelopes)

A BIG +1

Audacity does stuff... For free...

Some features could be added by VSTs. But some audio editing features would need to be integrated into a timeline-oriented view such as the view provided by Region Effects (like VVocal & Melodyne), or even just using RFX for an effect to preprocess a complete time interval to produce an effect.
Some examples that Izotope RX4 editor can do inside its own editor:
View & edit spectrum along a time line,
match eq,
match ambience,
dereverb,
denoise.

I have deleted a post in this thread because it was reported as being offensive.  Please follow the CoC and keep the conversation clean.

The main external audio editor I use is Izotope RX. So in terms of "what does that do that Sonar doesn't", well, that would be a 10,000 word essay, at least.
 
I do also use Sound Forge sometimes. And while I can't imagine a DAW catching up with what RX can do, I can imagine not needing SF any more. To get to that:
 
- Pencil tool for waveform re-drawing; really handy for manual removal of this and that kind of flaw and click
- better stereo to mono tool
- More sophisticated control over sample rate and bit depth conversion

BTW every DAW I've seen has a usable and decent drum maps UI as well, I'm on my hands and knees, can I please beg to get the existing functionality that isn't doing too well... running really well first before we move onto even more new features . I appreciate it may not be...as exciting... from a development standpoint, I fear existing functionality in need of a revamp/improved workflow is being left behind much like the Roland days and the concentration is focused mainly on new functionality. It would be depressing to think these issues are still hanging around in 2016. Sonar is a great product but the flimsy areas of functionality let it down. Thanks.
 
That aside I'm looking forward to the routing improvements you are peddling for future release....
 
OK the rest of you can ignore this... back to topic..

I use Sound forge for RMS normalizing and Adobe Audition to edit, reduce or level peaks in the waveform. Wave editors also merge projects for cross fading and cd marker placement. I'm thrilled that Cakewalk is asking this question!

Sound Forge - Batch processing, define regions, process according to regions.

Everything mentioned above by Craig, Dan, Kenny, Clint and Mike. Add to that list file analysis (e.g. average RMS, crest factor, overs, dynamics distribution, min/max sample values), test tone generation and file format conversion.