The TatukGIS Internet Server product was discontinued and replaced by the Developer Kernel ASP.NET edition (which is licensed per developer, not per server) in January 2014. For details, refer to the TatukGIS News article dated January 29, 2014.
For anyone still using the old Internet Server product:
The TatukGIS Internet Server product is licensed by server/computer, not by developed application and not by developer. So it is allowed to run two IS applications on a single server under one IS license. And it allowed for two developers to access and work with the IS product under a single license, provided that the IS is installed only on the one server computer.
Because the IS product is licensed by server, using a second copy of the same IS application on a complimentary or back-up server requires purchase of a separate IS license for each additional server computer.