Ubuntu – ny GUI tool for setting up an OpenVPN server

In short: OpenVPN Access Server is "almost free" and "just OpenVPN" (Community Edition) is totally free
However, they are configured in different ways. Open AS has indeed a web interface that simplifies (a lot) the tasks for setting it up. Open CE on the other hand, has to be configured by editing some configuration files
OpenVPN Access Server:
pros: very simple an intuitive configuration
cons: limited to two concurrent users. Although each additional one costs only nine USD a year, they are purchased in blocks of ten.
Some web features don´t work well (uploading your own CA certificate is one of them, so you still have to edit some files. See https://openvpn.net/index.php/access-server/docs/admin-guides/175-how-to-replace-the-access-server-private-key-and-certificate.html, method two)
OpenVPN Community Edition:
pros: completely free. Can have multiple concurrent users
cons: configuration is not a simple task
Conclussion:
If you can deal with the two users restriction, go for OpenVPN AS. If not, use OpenVPN AS for configuration and once working, switch to OpenVPN CE using such configuration as base. See Easy method of switching from Openvpn-Acess Server to Community Edition?

I got OpenVPN working. To answer my question:

There should be a server running like this:

$ ps auxww | grep openvpn
root       536  0.0  0.5  35672  5108 ?        Ss   00:47   0:00 /usr/sbin/openvpn --daemon ovpn-server --status /run/openvpn/server.status 10 --cd /etc/openvpn --script-security 2 --config /etc/openvpn/server.conf --writepid /run/openvpn/server.pid

In my case there wasn't due to a misconfiguration. It's fairly obvious, but for the record: to find openvpn problems in the syslog:

sudo service openvpn stop
sudo service openvpn start
sudo tail /var/log/syslog