The SharePoint Solution Installer has just been updated on CodePlex.
The installer allows you to easily provide MSI-like setup for your SharePoint solutions (WSPs) without having to write any installer code. All you have to do is set some values in a config file and ship the setup.exe, the config file, and your WSP.
The SharePoint Solution Installer was originally written by Lars Fastrup who recently wrote Inside the Index and Search Engines: MOSS 2007. The initial version handled features within the WSP scoped to the Farm. I recently updated it to handle features scoped to a site collection as well as provide some configuration and documentation links.
Several individuals have found this tool very useful – I hope you do as well. Lars was able to get the release out earlier today so I wanted to let others know that it is available.