App.Net was, I think, the closest we’ve come to a good Twitter alternative, and it came out back in 2012. It did basically everything Twitter did, but nicer. It had a decent web experience and a great selection of third party apps up and running within weeks of launch. And while it was a paid service (and maybe therefore doomed from the start), tons of people in the tech community went there and were having lively discussions. My App.Net feed was a joy to browse, and most of my Twitter friends were there. Oh yeah, and it was an app platform that let some devs build off their back end in interesting ways.
Plurk utilizes a horizontal timeline, with messages summarized by single verbs (“feels”, “loves”, etc.). As you would expect, media files can be shared, and Plurks can be liked. Emoticons are an important element of the Plurk user experience, and your selection increases as your karma grows. Karma is based on your activity on the social networking site. Group chat and direct messaging are also featured on Plurk.