Using Mac Pro 1.1 Today For Internet And Other Things.

Although OK for other tasks with software already installed, that model can run no higher macOS than v10.7 “Lion.” Most web pages today will not work under that macOS version. I have two newer Macs running 10.14 “Mojave” that are struggling with many web sites I visit.

So while you may find other ways to reuse it, it will be nearly useless on today’s internet.

A Mac Pro with a model identifier of MacPro1,1 would be the first Intel-based minitower – introduced in August 2006 and discontinued in January 2008.

You cannot install Sequoia on it. You can only upgrade it as far as Lion (10.7.*). Lion is thirteen major versions older than Sequoia and quite obsolete. Lion is so old that the browsers running under it are not likely to be able to handle either the security or the content associated with modern https sites.

While Tiger, Leopard, and Snow Leopard are not available for download, Lion is. Originally Lion required purchase of an activation key. I do not know whether Apple has removed the activation key requirement for the .DMG version.

Update macOS on Mac - Apple Support

If you are willing to learn a new OS, then perhaps try using Linux Mint on it. Linux is a great way of extending the useful life of older computers, but it does require learning a new OS. Linux is not for everyone though.

Linux Mint can use the current versions of many of the popular web browsers (Firefox, Vivaldi, Brave, Google Chrome) and has the free open source office suite LibreOffice installed by default. The Linux Mint software repository has access to lots of free open source software.

If you like video editing, even the Davinci Resolve software is compatible on Linux & I hear it works really well.

You can test drive Linux Mint by selecting the "Live" option when booting the Linux Mint USB installer. Performance will be extremely slow while booting & running from the USB stick, but it will give you a glimpse at what the default setup will look like.

If you decide to install Linux Mint, then make sure to first back up any important data on this Mac. If you need to access the data with Linux, then make sure the data is stored on a drive which Linux can access (exFAT is Ok). Also, make sure to have your macOS installer so that you can go back to macOS if you decide Linux is not for you.

Lion is the end of the line for your original Mac Pro.

Linux Mint is a great idea.

So, can I run 10.11 El Capitan on my Mac Pro 1.1 and access all of the internet?

No.

In 2015, researchers discovered that Secure Socket Layer (SSL) Internet encryption was not nearly as secure as was thought, and needed to be replaced. Internet encryption quickly moved to Transport Layer Security (TLS) which was rapidly deployed across the Internet. Over time, sites tightened requirements for what was acceptable for encryption.

Apple issued Safari version 9 in 10.11 El Capitan version of MacOS, which included TLS encryption. It was later provided by Security Update into the two previous versions of MacOS. 10.10 Yosemite and 10.9 Mavericks, PROVIDED you applied all available software updates.

MacOS versions older than those can not make a lot of secure [httpS:] connections on the Internet, because by todays standards, your proffered SSL encryption is considered inadequate.

A Mac that can't run 10.9 or later will not be able to do anything on the Internet.

Whatever you do, DO NOT Erase any running MacOS unless you have original Install discs.

Macs before about 2011 do not have ANY way to get a version of MacOS running without the original discs.