MariaDB is supported by Wampserver 3.0.7 and more
In order not to interfere with MySQL, the default port used by MariaDB is port 3307.
To allow the use of MariaDB, the relevant option must be validated in the Wampserver settings:
Right-click Wampmanager icon -> Wamp settings -> Allow MariaDB
But... still have to install a version of MariaDB 10.1.19 or upper of which you will find the installer on Sourceforge or on 'http://wampserver.aviatechno.net'

Once the MariaDB item appears in the Wampmanager menus, you can use it.
--- Some details about using MariaDB with Wampserver 3.0.7

--- PhpMyAdmin
PhpMyAdmin can be set to use either MySQL or MariaDB.
Just modify the file wamp\apps\phpmyadmin4.x.y\config.inc.php by declaring a second server with MariaDB.
When calling PhpMyAdmin, there will be the choice of the server: MySQL or MariaDB.

--- Contents of the file config.inc.php :
<?php

/* Servers configuration */
$i = 0;

$cfg['blowfish_secret'] = 'h]C+{nqW$omNoTIkCwC$%z-LTcy%p6_j$|$Wv[mwngi~|e'; //What you want

//Checking Active DBMS Servers
$wampConf = @parse_ini_file('../../wampmanager.conf');
//Check if MySQL and MariaDB with MariaDB on default port
$mariaFirst = ($wampConf['SupportMySQL'] == 'on' && $wampConf['SupportMariaDB'] == 'on' && $wampConf['mariaPortUsed'] == $wampConf['mysqlDefaultPort']) ? true : false;
if($wampConf['SupportMySQL'] == 'on') {
/* Server: localhost [1] */
	$i++;
	if($mariaFirst) $i++;
	$cfg['Servers'][$i]['verbose'] = 'MySQL';
	$cfg['Servers'][$i]['host'] = '127.0.0.1';
	$cfg['Servers'][$i]['port'] = $wampConf['mysqlPortUsed'];
	$cfg['Servers'][$i]['extension'] = 'mysqli';
	$cfg['Servers'][$i]['auth_type'] = 'cookie';
	$cfg['Servers'][$i]['user'] = '';
	$cfg['Servers'][$i]['password'] = '';

	// Hidden databases in PhpMyAdmin left panel
	//$cfg['Servers'][$i]['hide_db'] = '(information_schema|mysql|performance_schema|sys)';

	// Allow connection without password
	$cfg['Servers'][$i]['AllowNoPassword'] = true;
}
/* Server: localhost [2] */
if($wampConf['SupportMariaDB'] =='on') {
	$i++;
	if($mariaFirst) $i -= 2;
	$cfg['Servers'][$i]['verbose'] = 'MariaDB';
	$cfg['Servers'][$i]['host'] = '127.0.0.1';
	$cfg['Servers'][$i]['port'] = $wampConf['mariaPortUsed'];
	$cfg['Servers'][$i]['extension'] = 'mysqli';
	$cfg['Servers'][$i]['auth_type'] = 'cookie';
	$cfg['Servers'][$i]['user'] = '';
	$cfg['Servers'][$i]['password'] = '';

	// Hidden databases in PhpMyAdmin left panel
	//$cfg['Servers'][$i]['hide_db'] = '(information_schema|mysql|performance_schema|sys)';
	// Allow connection without password
	$cfg['Servers'][$i]['AllowNoPassword'] = true;
}

// Suppress Warning about pmadb tables
$cfg['PmaNoRelation_DisableWarning'] = true;

// To have PRIMARY & INDEX in table structure export
$cfg['Export']['sql_drop_table'] = true;
$cfg['Export']['sql_if_not_exists'] = true;

$cfg['MySQLManualBase'] = 'http://dev.mysql.com/doc/refman/5.7/en/';
/* End of servers configuration */

?>
--- End of file

For your connections to a database server to be done with MariaDB instead of MySQL, you must specify the port number.
Indeed, without specifying the port, it will be the default port that will be used, therefore 3306, so the default port assigned to MySQL.
Connection scripts use, for example:
$mysqli = new mysqli('127.0.0.1', 'user', 'password', 'database');
Or, in procedural terms :
$mysqli = mysqli_connect('127.0.0.1', 'user', 'password', 'database');

To connect with MariaDB, it is imperative to specify the port number:
$mysqli = new mysqli('127.0.0.1', 'user', 'password', 'database', '3307');
Or, in procedural terms :
$mysqli = mysqli_connect('127.0.0.1', 'user', 'password', 'database', '3307');

To check the connections on MariaDB, use the script:
wamp\www\testmysql.php by 'http://localhost/testmysql.php'
By having previously modified the script according to your settings, for example, if you did not set a password to root under MariaDB, the script must be:
<?php
/*    Using "mysqli" instead of "mysql" that is obsolete.
* Change the value of parameter 3 if you have set a password on the root userid
* Add port number 3307 in parameter number 5 to use MariaDB instead of MySQL
*
*     Utilisation de "mysqli" à la place de "mysql" qui est obsolète.
* Changer la valeur du 3e paramètre si vous avez mis un mot de passe à root
* Ajouter le port 3307 en paramètre 5 si vous voulez utiliser MariaDB
*/
$mysqli = new mysqli('127.0.0.1', 'root', '', '', '3307');

if ($mysqli->connect_error) {
    die('Connect Error (' . $mysqli->connect_errno . ') '
            . $mysqli->connect_error);
}
echo '<p>Connection OK '. $mysqli->host_info.'</p>';
echo '<p>Server '.$mysqli->server_info.'</p>';
$mysqli->close();
?>

--- Replace MySQL by MariaDB ---
Important note: It is imperative to back up your databases in SQL files by exporting them before disabling MySQL.
This is the only way to transfer your databases between MySQL and MariaDB.
-- How to replace MySQL by MariaDB --
- Change the port used by MySQL by 3308
Right-click Wampmanager icon -> Tools -> Use a port other than 3306
And put 3308 in the form "Enter the desired port number" then OK
And wait for green icon.
- Disable MySQL
Right-click Wampmanager icon -> Wamp settings -> Allow MySQL
So as to uncheck the line. Wait for green icon.
- Enable MariaDB
Right-click Wampmanager icon -> Wamp settings -> Allow MariaDB
So that the line is checked. Wait for green icon.
- Change the port used by MariaDB by 3306
Left-Click Wampmanager icon -> MariaDB -> Use port other than 3307
And put 3306 in the form "Enter the desired port number" then OK
And wait for green icon.

There you go ! MariaDB is now the default database manager.
Of course, you still have to import your previously backed up databases.