I've just created the forum titles I need for my community. They appear on the first page.

Is there a way to make one of those links to an external WWW site rather than internal forum?

It's possible with straight HTML. The last forum title on this community - "Full Demo Test" - is the same case. See the source code.

Look how we did it modifying main_forums.html template.

https://www.minibb.com/templates/main_forums.html

<table class="tbTransparentmb"><tr><td>{$user_logging}</td></tr></table>

<table class="forums">
<tr>
<td class="caption4" style="width:25px"><img src="https://www.minibb.com/forums/img/!pix.gif" style="width:25px;height:15px" alt="" /></td>
<td class="caption4" style="width:100%">{$l_forum}</td>
<td class="caption4" style="width:40px;text-align:center">{$l_num_topics}</td>
<td class="caption4" style="width:40px;text-align:center">{$l_replies}</td>
</tr>

{$list_forums}

<tr class="tbCel2">
<td class="caption1" style="width:5%;text-align:center"><img src="https://www.minibb.com/forums/img/forum_icons/qwerty.gif" style="width:16px;height:16px" alt="" /></td>
<td class="caption1" style="width:75%"><b><a href="http://minibb.org" target="_blank">Full Demo Test</a></b><br />Separate miniBB installation: almost all free and premium addons available, also as administrative demo access.</td>
<td class="caption1" style="width:10%; text-align:center"> </td>
<td class="caption1" style="width:10%; text-align:center"> </td>
</tr>

</table>