PHP

$a = 0.17;
$b = 1 - 0.83;
echo $a-$b; // [...]: -2.7755575615629E-17

Software requirements

MediaWiki
Roundcube : "The most common is MySQL but others are PostgreSQL and SQLite." [1]
NextCloud : "SQLite is the default database for Nextcloud Server and it is good only for testing and lightweight single-user setups without client synchronization. Supported databases are MySQL, MariaDB, Oracle 11g, and PostgreSQL, and we recommend MySQL/MariaDB." [2]
Baikal : "MySQL or SQLite" [3]
SabreDAV : no DB, but mod_php: "For maximum compatibility, apache 2 with mod_php is recommended. This is especially true if you plan to a file server. Card- and CalDAV servers run fine through FastCGI as well."
Agendav : "Most popular database backends are supported, such as MySQL, PostgreSQL or SQLite." [4]