user12639: Most video editing software allows me to import video of different frame rates, but Lightworks either does not have this feature still, or I cannot find it (on Lightworks or on the internet).  Does anyone have any tips?  I would really like to use Lightworks, but using multiple cameras (one of them being an iPhone), and shooting in slow motion, makes this a deal breaker.

user1871: Looks like you will need to transcode all clips with frame rates not matching the project's frame rate:

If the frame rate is of a clip is not compatible with your project, it
  displays in red.  You will be unable to import the clip into your
  project.  Clips with incompatible frame rates may be playable in a new
  project set to the  same frame rate as the clip.

(page 40; User Guide)
You can use ffmpeg, a command line tool, to transcode such clips with commands of the form
ffmpeg -i input.mp4 -c:v libx264 -crf 8 -r 25 -c:a copy -map 0 input25.mov

Edit: should make clear that 25 should be replaced with the framerate of the project. NTSC 30d i.e. 29.97 fps is denoted as 30000/1001 and 23.976 as 24000/1001. 

user35045: in the latest version it is now possible to import mixed framerates

12639: <p>Most video editing software allows me to import video of different frame rates, but Lightworks either does not have this feature still, or I cannot find it (on Lightworks or on the internet).  Does anyone have any tips?  I would really like to use Lightworks, but using multiple cameras (one of them being an iPhone), and shooting in slow motion, makes this a deal breaker.</p>
 1871: <p>Looks like you will need to transcode all clips with frame rates not matching the project's frame rate:</p>

<blockquote>
  <p>If the frame rate is of a clip is not compatible with your project, it
  displays in red.  You will be unable to import the clip into your
  project.  Clips with incompatible frame rates may be playable in a new
  project set to the  same frame rate as the clip.</p>
</blockquote>

<p>(page 40; <a href="http://www.lwks.com/index.php?option=com_lwks&amp;view=download&amp;Itemid=206" rel="nofollow">User Guide</a>)</p>

<p>You can use <a href="http://ffmpeg.zeranoe.com/builds/" rel="nofollow">ffmpeg</a>, a command line tool, to transcode such clips with commands of the form</p>

<pre><code>ffmpeg -i input.mp4 -c:v libx264 -crf 8 -r 25 -c:a copy -map 0 input25.mov
</code></pre>

<p><strong>Edit</strong>: should make clear that <code>25</code> should be replaced with the framerate of the project. NTSC 30d i.e. 29.97 fps is denoted as <code>30000/1001</code> and 23.976 as <code>24000/1001</code>. </p>
 35045: <p>in the latest version it is now possible to import mixed framerates</p>
