The Winows Installer (previously known as Microsoft Installer, codename Darwin) is an engine for the installation, maintenance, and removal of software on modern Microsoft Windows systems. The installation information, and often the files themselves, are packaged in installation packages, loosely relational databases structured as OLE Structured Storage Files and commonly known as "MSI files", from their default file extension. Windows Installer is a significant improvement over its predecessor, Setup API: several new features, such as a GUI framework, the automatic generation of the uninstallation sequence and the powerful deployment capabilities, made Windows Installer a viable alternative to stand-alone executable installer frameworks such as older versions of InstallShield and WISE (later versions of both products are based on Windows Installer) and NSIS.