I frequently use maxima (http://maxima.sourceforge.net/). Today I looked for related projects with GUIs.
wxMaxima is quite nice, it provides a good help at entering input.

But I miss writing mathematical sheets and just arrange the formulas and diagrams on it.

My first step to this is the php script at the end. I put my formulas in testformula1.txt, call the script php maxima2html.php >maxima2html.html and get a nice html output (at the left in the screenshot):

<style>
div.formula{
font-family: 'Lucida console', monospace;
font-size: small;
white-space: pre;
padding: 4px 1em;
margin: 2px;
clear: both;
float: left;
margin: 0px;
}
div.in{
border: 1px solid #FDD;
background-color: #D99;
margin-top: 5px;
}
div.out{
background-color: #9D9;
margin-left: 2em;
margin-bottom: 1px;
}
</style>
<?php
function cleantext($text){
$re = '/\(%[io][0-9]*\)/';
$ntext = preg_replace_callback(
$re,
create_function('$matches','return str_repeat("",strlen($matches[0]));'),
$text);
$ntext = str_replace("\t",str_repeat(' ',8),$ntext);
$lines = explode("\n",$ntext);
$padleft = NULL;
// find smallest intend
foreach($lines as $l){
$i = 0;
while($i<strlen($l)){
if($l[$i]!=" "){
if(is_null($padleft) or $i<$padleft){
$padleft = $i;
}
break;
}
$i++;
}
}
for($i=0;$i<count($lines);$i++){
$lines[$i] = substr($lines[$i],$padleft);
}
$nntext = join("\n",$lines);
return rtrim($nntext);
}
function readOutput($pipe){
$out = '';
$shell = '(%i';
while(!feof($pipe)){
$out .= fgetc($pipe);
if(substr($out,-strlen($shell),strlen($shell)) === $shell){
while(substr($out,-1,1)!=')')
$out .= fgetc($pipe);
break;
}
}
return $out;
}
function machflecken($pre, $class, $continue = false){
if(empty($pre)) return;
echo '<div class="formula '.$class.($continue?' continued':'').'">';
echo $pre;
echo '</div>',"\n";
}
$in = file('testformula1.txt');
$in[] = 'quit(a=b);';
$descriptorspec = array(
0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
);
$out = '';
$process = proc_open('maxima -q', $descriptorspec, $pipes);
if (is_resource($process)) {
$out = cleantext(readOutput($pipes[1]));
machflecken($out,'start');
while(true){
if(empty($in)) break;
$cmd = array_shift($in);
fwrite($pipes[0], $cmd);
#print 'in: '.count($in).': '."\n".$cmd."\n";
$out = cleantext(readOutput($pipes[1]));
if(FALSE === strpos($cmd,'=')){
machflecken($cmd,'in',true);
machflecken($out,'out');
}else{
machflecken($out,'out');
}
}
stream_get_contents($pipes[1]);
fclose($pipes[1]);
$return_value = proc_close($process);
#echo "command returned $return_value\n";
}
?>