Erick Hitter

WordPress 3.0 introduced a native shortlinks feature, which builds URLs using query strings. This plugin converts those URLs to ones using pretty permalinks, which makes for a nicer-looking URL and improves shortlinks’ ability to be cached.
Posts and pages are supported by default, while filters make it possible to support other post types.
For example, https://example.com/?p=123 becomes https://example.com/p/123/.

ETH Simple Shortlinks

Convert WordPress's query-based shortlinks to pretty permalinks that are cacheable. https://example.com/?p=123 becomes https://example.com/p/123/.

Denis Lam

WordPress generates shortlinks for your posts and pages. By default it uses the <code>?p=</code> with the post ID added to it, but if you have a rather long domain name this isn’t very useful. If you use <a href="http://bit.ly" rel="nofollow ugc">Bit.ly</a>, this plugin will help you replace the shortlink WordPress generates with a proper Bit.ly shortlink.
This plugin uses the latest Bit.ly OAuth 2 draft specification API instead of its deprecated V3 API and enables you to use generic access token to automatically enable Bit.ly shortlinks in your entire multisite network without the need for each site user to have to tinker with any settings or authentication configurations.

Bit.ly Shortlinks Multisite (Uses OAuth 2 API)

This plugin replaces the default WordPress shortlinks with Bit.ly shortlinks for your single site or multisite WordPress network.

ETH Simple Shortlinks vs Bit.ly Shortlinks Multisite (Uses OAuth 2 API)