DuckDuckGo is a competing search engine to Google that focusing on increasing search productivity while protecting user privacy.
Ranked in these QuestionsQuestion Ranking
Pro Very protective of user privacy
Pro Allows searching from specific sites using bangs
Bangs are commands that allow searching via a different website's local search engine, using keywords or abbreviations with an exclamation mark (!). For example searching "world war ii !wiki" will automatically redirect to Wikipedia.org and show results for the query "world war ii" there, instead of DuckDuckGo, using Wikipedia's search engine.
The more common sites have shortened alternatives for these commands. Such as !g for Google, !i for images and !yt Youtube.
The whole list of bangs can be found by typing "!bang" in DuckDuckGo.
Pro Has a wide spectrum of instant answers
For select queries DDG pops up a box that supplies the exact answer. For example, searching "stopwatch" will pop up a stopwatch, asking for "words like..." will show a list of related words, typing "password" will generate a password, etc.
Pro Can disable advertisements
The search engine allows freely disabling ads.
Pro Ads are non-obstructive and don't track you
The ads are clearly labelled as ads and are non-obstructive. The ads are based on the searched keywords and there's no tracking involved on their visibility. You just need to remember that the site the ad links to might track you.
Pro Many customization options for appearance
DDG allows customizing almost any aspect of the search engine's appearance including fonts, page width, alignment, header behavior, site icons, etc and has a selection of premade themes available as well.
Pro Infinite scroll of search results
DuckDuckGo results page is an infinite scrolling page, so you don't need to be clicking through pages.
Pro Pulls information from multiple search engines
DDG searches through not only its own database but pulls search results from multiple other search engines, including Google, Bing, Yahoo, etc for a total of 30+ search engines as well.
Pro Has a .onion site
Only accessible from Tor.
Of course, it's nicer when enabled, but it's not required. Some browsers are too limited (mobile, terminal) or turn it off for security reasons (tor, etc.), and DDG still works.
Pro Built-in WOT (Web Of Trust) icons
WOT is a free, community-run website review system, to help protect against spam and malicious websites. Duckduckgo provides the option to display WOT icons next to website URLs, to indicate their ratings, without requiring additional addons to be installed.
Con Doesn't do personalized searches
Since they don't track you the results are not tailored to your interests.
Con Form over function (overall search experience is poor)
It's nice to adjust the settings and all but after a couple of days you will want to go back to a more functional search engine.
Sure DDG looks shiny and !bangs are great but many wouldn't consider it as a viable alternative. Better results for search queries is more important than fancy looking CSS.