I was tossing around the idea of setting up 2-factor authentication for a couple of my web apps and I was looking at the community edition of WiKID
http://www.wikidsystems.com/community-version
I checked the Linode library and didn't see anything on it.
I haven't used WiKED, but I am starting to implement Yubikey One-Time Passwords. They have a simple web API or you can run your own OTP system with their keys.
You can mention users to notify them: @username
You can use Markdown to format your question. For more examples see the Markdown Cheatsheet.
> I’m a blockquote.
I’m a blockquote.
[I'm a link] (https://www.google.com)
I'm a link
**I am bold** I am bold
*I am italicized* I am italicized