Does anybody are conscious of how, in wordpress, I possibly could implement many calendars on the site, each only highlighting days which are inside a specific category? I'm wishing to create multiple calendars, each monitoring all the occasions using their own cat.

After researching for some time the very best I possibly could find was this thread:

http://wordpress.org/support/topic/266627?replies=11

However it appears to peter out before there's ever a functional solution

Things I have below spits the days in the present month and links (towards the day's archive page) days with posts from the certain category. Just duplicate the code for every cat you need to display. To become functional, you will need to then add conditional formatting allow it nice calendar rows and most likely expand the script to pay for multiple/partial several weeks, but this will enable you to get began.

<?php 

$today = getdate();
query_posts( 'category_name=mycat' . '&year=' . $today["year"] . '&monthnum=' . $today["mon"] );  // query_posts() is a WP function

if ( have_posts() )
{
    $postDates = array();
    while ( have_posts() )
    {
        // The if/while we're in now is called the "WordPress Loop"

        the_post();  // Sets all the WP variables up for the current post
        $postDates[] = (int)(the_date("j", "", "", FALSE));  // the_date() is a WP function
    }

    for ( $i = 1; checkdate ( (int)(date("n")), $i, (int)(date("Y")) ); $i++ )
    {
        // checkdate() is a PHP function which validates a date against the gregorian calendar
        if ( in_array($i, $postDates) )
        {
            echo "<a href=\"" . get_day_link('','',$i) . "\">" . $i . "</a> ";  // get_day_link() is a WP archive function 
        }
        else
        {
            echo $i . " ";
        }
    }
}

wp_reset_query();  // Resets the WP variables so everything's back to normal

?>

HTML output:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 <a href="http://www.myblog.com/2010/04/17/">17</a> 18 19 20 21 22 23 24 25 26 27 28 29 30