Wavosaur

[_safari_]

Time stretch?

[xpander]

Sure.

Standalone or VST
With or without the pitch change
Live input/output or offline processing (consideration with other apps)
Whole tracks or partial edits
Small or extreme changes
"Classic" sampler style (quality) or pristine audio
For free with more or less work and varying results or for (big) money
and relative ease of use

...now those are some of the questions to ponder.

Native? The devs have said not yet. Search.

Elastique
http://products.zplane.de/index.php?page=elastiquepitch
(as used by many editors/daws)
http://www.zplane.de/index.php?page=description-elastique
SoundTouch
http://www.surina.net/soundtouch/soundstretch.html
Prosoniq Timefactory
http://www.prosoniq.com/editing-products/timefactory-2/
Dirac
http://dirac.dspdimension.com/Dirac3_Technology_Home_Page/Dirac3_Technology.html
Celemony Melodyne
http://www.celemony.com/cms/index.php?id=products_essential&L=0
Antares Auto-Tune
http://www.antarestech.com/products/auto-tune-7.shtml

Paul's Extreme Sound Stretch
http://hypermammut.sourceforge.net/paulstretch/
Akaizer
http://akaizer.blogspot.com/
Sknote Traks
http://www.sknote.it/download.htm
DBlue Glitch
http://illformed.org/plugins/glitch/

Samplers.