<table>
<tr>
    <th>Atividade<th>
    <th>Usuario</th>
    <th>Data/Horario</th>
</tr>

    <?php
$a = 0; $b = 0;
while($a < 10){
echo '<tr>';
echo '<td>'.$tabela[$a][$b].'</td>';
echo '<td>'.$tabela[$a][$b+1].'</td>';
echo '<td>'.$tabela[$a][$b+2].'</td>';
echo '</tr>';
$a++;
}
?>
</table>