Open a RAR or a 7z
Drop the archive and see straight away what is inside: download one file or all of them. It works with .rar, .7z, .tar.gz, .tar.xz and .zip, and everything happens in your browser.
Why a .rar is a wall
A .zip opens on Windows, on a Mac, on Android and on an iPhone with nothing installed. A .rar and a .7z do not: they are formats belonging to programs that have to be installed, and whoever gets the attachment on a phone, on a Mac or on a work computer where nothing can be installed is stuck. The road nearly everybody takes is to upload the attachment to some website, which for a contract or a payslip is exactly the opposite of what is needed.
Here the archive does not go anywhere: it opens in the browser, you look at the list and download what you need. The engine that does it is a library compiled to WebAssembly, it weighs about a megabyte and it is downloaded only at the moment you actually open an archive, not on every visit.
What it opens, and what it does not
It opens .rar, .7z, .tar.gz, .tar.xz and .zip, with accented names and names in Chinese characters in the right place, and with nested folders. It also opens zips with a password, which is the gap the zip page declares it cannot close: there it says you need a program on a computer, here the password is enough.
What it does not open is a 7z with encrypted content: the engine running here does not have that piece, and the page tells you so rather than handing you a broken file you would only discover on opening. For those you need 7-Zip on a computer. And if the 7z has the file names encrypted as well, without the password you cannot even see the list: the page recognises that and says it, because otherwise it would just look broken.
The file that arrived half-way, and huge archives
If the list comes out empty it does not mean the archive is odd: nearly always it means it arrived incomplete, that is the download stopped. The page says so and sends you to download it again, rather than letting you believe an empty list or handing you half the files.
On very large archives there is an honest limit worth knowing: to pull out a single file, some archives force everything to be decompressed, and everything goes through the browser's memory. Above a few hundred megabytes the wait shows and a program on a computer is the better road. The limit is not a whim: it is how those formats are built.
The border with zip, said in both directions
If what you have is an ordinary .zip, it opens here all the same, but the short way is Open a ZIP file: it is a lighter page that does not have to download a one-megabyte engine to do something the browser already knows how to do. When you drop a zip, this page tells you and sends you there.
The reverse holds too: if you open a zip and realise it is actually a .rar, the other page now points here instead of ending in a dead end. And if what you need is not opening but creating an archive protected by a password, that is a different job and it lives in Create a ZIP with a password.