Convert VMware Image .vmdk to VirtualBox Image .vdi

To convert VmWare appliances to VirtualBox you can use this command :

VBoxManage clonehd clone.vmdk ./clone.vdi -format VDI

Then you can Add it to VirtualBox using the "New" button (see image)

Then, 

- Click Next.

- Enter a name for the Virtual Machine.
- Select Linux as the operating system and Debian as the Version.
- Click Next.

- Change the default memory settings if you wish, if you are unsure leave it unchanged.
- Click Next.

- Select "Use existing hard disk"

- Click on the browser icon next to the drop down menu and choose clone.vdi

If you had some problems in xserver, those steps [1] will resolve it:
1. start virtual machine 
2. pressing ESC at "GRUB loading please wait" 
3. select "recovery mode" 
4. pressing multiple times (maybe only one is enough) 
5. command prompt is displayed. I executed command: 
dpkg-reconfigure xserver-xorg 
6. xserver console pops-up: I just went through the wizard and select only!!!! default. 
7. After finishing program returns back to command prompt. I executed command: reboot 
8. Ubuntu reboots - don't touch anything - it reboots fine. 

Good luck!!

[1] https://forums.virtualbox.org/viewtopic.php?t=18