Access Web App on Linux Server via Ethernet Cable Without Router

One option is to change the network adaptor of the virtual machine to bridged mode; you should then be able to access the virtual server from the other machines on the network, by providing your guest's IP address.

Edit:

For practical aspects, look at the VirtualBox documentation on Virtual networking. Your options are to use bridged networking

With bridged networking, VirtualBox uses a device driver on your host system that filters data from your physical network adapter. This driver is therefore called a "net filter" driver. This allows VirtualBox to intercept data from the physical network and inject data into it, effectively creating a new network interface in software. When a guest is using such a new software interface, it looks to the host system as though the guest were physically connected to the interface using a network cable: the host can send data to the guest through that interface and receive data from it. This means that you can set up routing or bridging between the guest and the rest of your network.

or port forwarding:

As the virtual machine is connected to a private network internal to VirtualBox and invisible to the host, network services on the guest are not accessible to the host machine or to other computers on the same network. However, like a physical router, VirtualBox can make selected services available to the world outside the guest through port forwarding. This means that VirtualBox listens to certain ports on the host and resends all packets which arrive there to the guest, on the same or a different port.

So, in case of a NAT port forwarding, you should use the following command:

VBoxManage modifyvm "VM name" --natpf1 "guesthttp,tcp,,80,,80"

I don't know about your particular ISP, but I am pretty sure most ISPs block port 80. Here are some things you can try.

First, you can verify that your router is accessible from the internet. Most router firmwares allow some form of "remote access" . Pick a random port, beyond 8000, say 8680. Then, verify that you are able to access the router at http://your.actual.ip.address:8680. If this opens up your router page, you are on the right track.

Next, try changing the port. You don't have to mess with the server, just forward port 8700 externally to 192.168.2.64:80 internally. Try accessing http://your.actual.ip.address:8700 and that should reach your server.