When reaching the final install step in the phpBB 3.1.6 installation, you will click the last button before being informed that the installation is succesfull and you can enter the ACP. Then you will get a httpd 500 error.

This is not a problem on phpBB 3.2-dev and is related to php7.

Apache2 error log.

[Fri Dec 04 12:20:46.346342 2015] [:error] [pid 2070] [client 192.168.1.90:46786] PHP Fatal error:  Cannot use 'null' as class name as it is reserved in /var/www/html/phpBB3/phpbb/cache/driver/null.php on line 19, referer: http://192.168.1.98/phpBB3/install/index.php?mode=install&sub=create_table