user-1: Some FC's say that they support cleanflight and have no mention of Ardupilot. Is this just because its what's recommended or because it's all that works?

user57690: There are pre-built binaries for many flight controllers. 
http://firmware.ardupilot.org/ lists out the different ardupilot builds (arducopter, arduplane, etc.) and by clicking on them , you can see the different versions, then the different builds per version.
This document goes into more detail on the file structure they use for pre-built binaries.

-1: <p>Some FC's say that they support cleanflight and have no mention of Ardupilot. Is this just because its what's recommended or because it's all that works?</p>
 57690: <p>There are pre-built binaries for many flight controllers. </p>

<p><a href="http://firmware.ardupilot.org/" rel="nofollow noreferrer">http://firmware.ardupilot.org/</a> lists out the different ardupilot builds (arducopter, arduplane, etc.) and by clicking on them , you can see the different versions, then the different builds per version.</p>

<p><a href="http://ardupilot.org/dev/docs/pre-built-binaries.html" rel="nofollow noreferrer">This document</a> goes into more detail on the file structure they use for pre-built binaries.</p>
