It's free if you just want to reserve a username and add an RSS feed from your own website - which can be either full articles (which will appear in Micro.Blog as a title & link), or short 280 char posts. You can reply to posts with a free account too.
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EDIT: Probably easier if for the other plans I just post the site's own info:
New Microblog — $5/month
We'll create and host a microblog for you at username.micro.blog or your own domain name. Includes cross-posting, pages, themes, and publishing from the web, iOS, and Mac.
New Blog + Microcast — $10/month
All the features of a hosted microblog plus audio hosting. Upload MP3s via the web or use the companion iPhone app Wavelength to record and edit your own microcast. We'll create a podcast feed for your site.
Enable Cross-posting — $2/month
Already have your own microblog? Add Twitter, Medium, LinkedIn, and Facebook cross-posting via Micro.blog. Works with any RSS feed.
Give Micro.blog
Invite someone to Micro.blog or pay for their first year of blog hosting.
-------
EDIT: Probably easier if for the other plans I just post the site's own info:
New Microblog — $5/month
We'll create and host a microblog for you at username.micro.blog or your own domain name. Includes cross-posting, pages, themes, and publishing from the web, iOS, and Mac.
New Blog + Microcast — $10/month
All the features of a hosted microblog plus audio hosting. Upload MP3s via the web or use the companion iPhone app Wavelength to record and edit your own microcast. We'll create a podcast feed for your site.
Enable Cross-posting — $2/month
Already have your own microblog? Add Twitter, Medium, LinkedIn, and Facebook cross-posting via Micro.blog. Works with any RSS feed.
Give Micro.blog
Invite someone to Micro.blog or pay for their first year of blog hosting.