Polr - An open source URL shortener. A great non-profit and free alternative to bit.ly, TinyURL, or goo.gl.
YOURLS - YOURLS is a website that contains all the tools you need to create and launch your very own URL shortener. URL shorteners like bitly or TinyURL are fine for public use, but they offer limited options in terms of URL customization.
Anonymous URL Shortener - Anonymous URL Shortener, Referer, Anonymizer, Redirection service.
Bitly - Get the most out of your social and online marketing efforts. Own, understand and activate your best audience through the power of the link with Bitly Enterprise.
Shlink - A self-hosted URL shortener
Zapier URL Shortener - Zapier is an online platform that offers unique services related to URLs, including the shortening of URLs.