There are actually a few options here. Below is a list of software for computers running Windows, I am uncertain if there are MAC OSX or LINUX equivalents.
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Adobe Photoshop CC ($19.99 per month)
Adobe Photoshop CS6 (Discontinued, no official link)
Autopano (Free
?)
GIMP (Free
and open source!)
Image Composite Editor (Free!)
PTGui ($87 for personal-use license)
Photosynth (Discontinued, no official link)
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As far as the discontinued software goes, you will have to search for them yourself as I cannot provide legitimate links for them. If you are
truly serious about panoramic photography like myself, PTGui is the best I've ever used. It
is a bit pricey, but very much worth it. You get lifetime updates for free as well. PTGui also includes an excellent (and free) viewer that works very well. You also have a couple of android options.
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AutoStitch Panorama Pro (Discontinued, $1.99)
TurnMe Panorama (Free!)
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As far as AutoStitch goes, you
might still be able to acquire it through the link I provided. I can still view the app because I purchased it while it was available, but I've never tried opening a discontinued app link in an account that did not download or purchase said app. It is worth the price, you can directly shoot a panoramic photo or stitch existing photos. TurnMe Panorama isn't a stitcher, but the best mobile panorama viewer I have had the pleasure of using. There are many other options for android, but these two are my favorites. Just search
"Panorama" or
"Panoramic" on the play store, and you will get plenty of results. Hope this helps.