Existing Micropub API endpoint implementations.
Examples of IndieWeb sites that support the micropub API (in order of deployment).
Aaron Parecki supports publishing various post types on aaronparecki.com using micropub since 2013-12-25.
- 2013-12-25 note micropub publishing support added
- 2013-12-28 pushup micropub publishing support added
- 2014-02-24 photo micropub publishing support added
- 2014-09-17 bookmark micropub publishing support added
- 2014-11-07 repost micropub publishing support added
- 2014-12-22 like micropub publishing support added
Ben Roberts posts to his Postly site via micropub. Photos are posted using OwnYourGram and Notes, Replies, and Articles are posted using his own Postly Client. Deleting entries via micropub added 2014-09-28.
bear supports micropub since 2015-01-01.
- Supports any post types by passing all metadata in the 'content' param as and inferring post types from it (so all a client needs is a content field).
- Supports edit over POST via resending content (+ metadata) and the slug of the post to be edited.
Jeena Paradies supports micropub for notes (with syndication and reply-to) only since 2015-07-12. Posting photos works too since 2015-07-24. And now even person tagging for notes and photos since 2015-07-30.
- Supports any post types by and inferring post types.
Micropub has been added to the following CMS software and blog publishing tools for additional server support.
Ben has written a Known plugin that logs in via IndieAuth and publishes content via micropub. It's designed to work so that all indieweb post types - notes etc - are passed to the content plugin registered to handle them. 
wordpress simple-location plugin needed to display location info.
Shane has written a Craft plugin for Micropub. It currently only works with notes and requires some configuration to setup. It has also only been tested with Quill so far, as of 2015-07-11. https://github.com/ShaneHudson/Micropub_Craft
Pelle Wessman has written a self-hosteable service that exposes a Micropub endpoint and then performs the instructions sent to that endpoint by committing Jekyll formatted data to a GitHub repository for the Jekyll site. Modular built and would be possible to extend to support other systems like Jekyll as well. https://github.com/voxpelli/webpage-micropub-to-github
Sebastiaan Andeweg wrote a Micropub plugin for Kirby. As of 2016-12-12 it supports posting with FormEncoded and JSON, and has a branch for update (replace and add) that needs some cleaning and 'delete' support before it can be merged. (I'm selfdogfooding it anyway now) https://github.com/sebsel/kirby-micropub
Ryan Barrett's ownyourresponses is PESOS as a service for Twitter favorites, retweets, and replies and Instagram likes. It polls your accounts periodically for new activity via the APIs and creates corresponding like, repost, and reply posts on your site via Micropub.
The original motivation is described in PESOS for Bridgy Publish.
How much of the Micropub specification is implemented by open source software projects.