There are a number of software based Windows iSCSI Target options available, the majority of which require a licence. Some vendors provide a free license version for personal use - which may have reduced functionally. Target options include, but are not limited to, the following -
Kernsafe iSCSI SAN - a free version is available for download (iStorage Server Free) - you will need to register for an account in order to apply for a free license. Registering for an account is relatively straightforward - at the time of writing it's possible to download a 20-day trial version without registering.
StarWind Virtual SAN - a Free license/version is available. Personally I found it very difficult to register and obtain a free license as a corporate email address is required.
pyTarget - "...Implement a powerful iSCSI target in python, easily use under most popular systems. ..." - a standalone binary is available for Windows 32-bit (will run without python environment). This project does not have a GUI, however it can be configured from a web interface. Alternatively a .xml configuration file can be used.
SANDeploy Server - 30 day trial. Two version are available - SANDeploy Server and SANDeploy Boot Server (which includes DHCP and TFTP server).
Installing and configuring all of the iSCSI Targets listed above is beyond the scope of this guide - I have however included some instructions for Kernsafe iStorage Server (see here), Microsoft iSCSI Software Target (here) and pyTarget (here).
NOTE
- some Targets will only allow authenticated connections - Client/Host system identifiers may need to be specified for connections to be made. pyTarget for example will only allow connections from a Client/Host whose IQN has been added to a filter list. Microsoft iSCSI Software Target 3.3 also requires Client/Host identification.