Question: I am really struggling to find compatible software that will allow me to animate PNG files. The GIMP plugin crashes my GIMP. Nothing else supports it. Is there any way I can easily put together the frames of a few PNG files and animate them as an MNG?

Answer: 
One way is to use a tool like ImageMagick. Which is available free of charge.

> 
> You can read more than one image from a sequence with a frame range. For example, you can 
>  extract the first four frames of an image sequence:
> 
> 
> 
> ```
> $ convert 'images.gif[0-3]' images.mng
> 
> ```
> 
> 

<http://www.imagemagick.org/script/command-line-processing.php>

If you have frames in separate file, I'm pretty sure you can use a command something like

```
$ convert image_1.jpg image_2.jpg image_3.jpg images.mng

```

or

```
$ convert -append image_*.jpg images.mng

```

but note I have not tried this. I'm not sure if you need the `-append` option.
You can try Format Factory. Its a nice software that supports video and image converting. Just download the latest version and convert your image to desired format. I use this software for converting videos and images.