There are some programmers that like to use MSI installers to pack their programs when the program doesn't really need installation. If you want to view or extract the contents of MSI files, you can try the solutions in this article.
When deciding which archiver is best for you, two things to consider are how well it can compress files and how quickly it performs. Here we test 15 different file compression programs to find out who's got the fastest speeds and which archivers create the smallest files.
Although 7-Zip is the most popular free archiver software, the current stable version has a nasty bug where an image cannot be opened directly from an archive reporting that the file has been deleted or location isn't available.
Here we have 7 free tools that can auto extract multiple archive files, even if they are all protected by different passwords. You supply all the required passwords to the program and it will do the rest.
To convert from one format to another isn't difficult and you can install an archiver, extract the files and re-compress them to the new format. There are other ways to conveniently convert from one archive format to another though, here's a few to look at.