I took this one-page PHP script from a forum with no attribution. I altered the parsing of wiki words so that it would convert more urls into working links.

First character is space, this is monospaced.
four dashes give you a horizontal rule.
first char is dash, then space, the line is a bulleted list.
wiki page links are marked with a tilde as the first character. Just make sure you only use characters in the link that are legal for filenames.

<?php 
function p($c)
  {
    $r=preg_replace(array(“~^ +([^\n]+)~m”,'~^-\s+(.*)$~m',“~-{4,}\r?\n~”,'~(http(?:s)?)://([\S]+)~i','~\n~'),array('<code>$1</code>','</pre> <ul> <li>$1','
---
','[[$1://$2][$2]]','<br />'),$c); preg_match_all('/~\w+/',$r,$x); foreach(array_unique($x[0])as$m){$r=str_replace($m,x($m)? “[[?$m][$m]]”: “$m[[?e=$m][?]]”,$r); } return$r;  } function f($f) { @mkdir('wik'); return @file_get_contents(“wik/$f.w”); } function b($b) { echo“
---+ [[?$b][Backlinks $b”.“]]
<div id='c'>”; foreach(glob('wik/*.w')as$f){$f=substr($f,4,-2); if(strpos(f($f),$b)!==false)echo“[[?$f][$f]]<br />”; } echo“</div> ”; } function x($f) { return file_exists(“wik/$f.w”);  } function e($p) { $p=$p?$p:$_GET['e']; echo“
---+ Edit”.“ $p
<form action='?$p' method='post'><textarea cols='50' name='c' rows='10'>”.f($p).“</textarea><br /><input type='submit' value='Save'></input>”; } $p=preg_replace('~(e|b)=(.*)~','',$_SERVER[QUERY_STRING]); $c=$_POST[c]; $e=$_GET[e]; $b=$_GET[b]; if(!$p&&!$e)$p='~<a href='https://xenos.quix.us/explorers/jasonnemrow/private/mainpage' rel='nofollow' title='explorers:jasonnemrow:private:mainpage'>MainPage</a>'; if($c){@file_put_contents(“wik/$p.w”,htmlspecialchars($c)); header(“Location: ?$p”); } echo“WW”; if(!$e) { if(!$b) { echo x($p)?“
---+ [[?b=$p][$p]]
<div id='c'>”.p(f($p)).“</div>
---
[[?e=$p][”.“Edit]] | <small>Modified: ”.date('d.m.Y @ H:i:s', @filemtime(“wik/$p.w”)):e($p); } else b($b); } else e($e);</small></form></li> </ul>