OpenVPN Access Server is commercial version with admin web interface. It come free for 2 client connections but more than that need to be paid. Simplified installation process.
OpenVPN (community version) is free but need to be manually installed, without admin web interface but once you set it up it's basicly the same functionality as OpenVPN Access Server but without connections limit.
If you want it simple but don't require more than two connections you will use OpenVPN Access Server. If you need more than two connections for free but aren't scared of manual installation you will use OpenVPN community version.