7-Zip is licensed under GNU LGPL, and the *.7z format has support across all major operating systems. There should be no trouble opening the archives under any operating system, and no need to deal with messages bugging you to register or pay for the app. Source code can be found here.
Powerful features allow automation of common tasks. For example archives with applications in them can be extracted to the desired Application folder, then the archive itself will be placed in the trash, and BetterZip will exit all with the click of a button. Applescript can also be used to do more