Downloading ISSI 5.1.9 from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this software available. The program lies within Development Tools, more precisely Distribution.
ISSI is compatible with Windows XP/Vista/7/8/10/11 environment, 32-bit version. This free software is an intellectual property of albartus.com. We recommend checking the downloaded files with any free antivirus. The most popular version among the program users is 5.1.
From the developer:
In the past adding some customization to Jordan Russell's Inno Setup one had to look for pieces of code and implement them into their own script. Now with this new generation of ISSI it's possible to add prefab functionality to Inno with just a few lines of code. These includes use the basic include functionality to quickly add and remove various customization.
You may want to check out more software, such as Parallels Workstation, IBM Rational Clearquest or SiteInFile Compiler, which might be similar to ISSI.