An OptiSurface Designer license can only be used on one computer. However, you can easily purchase another license (at the normal low starter pack price) to install the software on another computer.
After that, credits can be bought for multiple computers from your single web store account but once the credit pack is activated on one computer those credits will only be available to use on that computer.
Also, you can unlock a field design on one computer and then email that .osd file to your other computer (or anyone else who has the same version of OptiSurface Designer) and then open the .osd file and the design will still be unlocked.
