WordPress has evolved so much through out the years beginning as a blog platform, it has moved towards becoming one of the best CMS outside. Today you could use WordPress with much greater use and most of the people using it is because of the plugins that is widely available, ease of use and also SEO friendly.
1. WordPress as Shopping Cart

We have some free WordPress Shopping Cart or we could opt for the commercial theme Shopperpress. Depending on functionality and the complexity of the cart you are looking for.
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2. WordPress as Classifieds Website

I own a Classifieds and greatly regret that WordPress Classifieds was not out earlier like 5 years back.
[Open Classifieds - Free Classifieds Plugin]
[Classipress - Premium Theme]
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3. WordPress as Directory

[DirectoryPress - Premium Theme]
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4. WordPress as Review Website

[WPReviewSite]
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5. WordPress as Real Estate Website

Yup, you can transform WordPress to allow others to publish their properties. This Real Estate WordPress Theme actually adds some great search features to make this a great theme. I bought one and my website is at PropertyTrade.my
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6. WordPress as Coupon Website

[ Couponpress - Premium ]
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7. WordPress as Geo Location Website

I am not sure how to mentioned this but you can simply use this WordPress Theme as a service review, tourism website, or simply an event website.
[Geo Location Website - Premium]
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8. WordPress as Events Website

[ WordPress Events - Premium ]
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9. WordPress Portfolio

[ Sharpfolio - Free]
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10. WordPress Job Board

[ Job Board - Premium ]
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11. WordPress Wiki

[ WordPress Wiki Theme - Premium ]
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12. WordPress Auction

[ WP Auction - Free & Premium ]