They're two little extension for very distinctive purposes. VLD is a tool for hard core PHP hackers that want to figure out what is going on in PHP's engine. This would be an extremely useful tool for students that want to work on the Google Summer of Code project to implement and finish "Ilia's" Optimizer .

The translit extension focuses on transliterating scripts into different representations. It contains many filters for different tasks. For example the "normalize_numbers" filter can convert "１２３４５６７８９０" into "1234567890" with the following script:

<?php
$input = "１２３４５６７８９０";
var_dump(transliterate(
    $input,
    array('normalize_numbers'),
    'utf-8', 'ascii'));
?>

But many other filters exist, such as converting Chinese text (大平矿难死者增至66人) to pinyin (dapingkuangnansǐzhezengzhi66ren) or stripping out accents (á -> a )and converting ligatures (© -> (c), æ -> ae) etc. The translit extension is also used on this website to create "nice" urls with the following code:

$blurp['url'] = transliterate($blurp['title'],
    array(
        'cyrillic_transliterate', 'lowercase_latin',
        'normalize_ligature', 'diacritical_remove',
        'normalize_punctuation', 'remove_punctuation',
        'spaces_to_underscore', 'compact_underscores'),
    'utf8', 'us-ascii');

Both extensions are available through PECL and installable like:

pecl install vld
pecl install translit