What are some alternatives?
When comparing p7zip and The Unarchiver, you can also consider the following products
WinRAR - WinRAR is a powerful archive manager.
PeaZip - Free file archiver utility, free Rar files software. Open, extract 7Z ACE CAB RAR TAR ZIP archives, support 180+ formats. Data compression and encryption tool.
Bandizip - Bandizip : All-In-One Free Zip Archiver. Bandizip is a lightweight, fast and free All-In-One Zip Archiver.
WinZip - The world's best file compressor in the world.
File Roller - File Roller is an archive manager for the GNOME desktop environment.
FreeArc - FreeArc is a free and open source file archiver developed by Bulat Ziganshin.