There are flavors (variations) of GNU/Linux that work well with older hardware, and which will breathe new life into that laptop or PC that came with Xp. Best of all they are
FREE! yet have a robust support network (the dimminishing levels of which MS and Apple are famously known for after having sagged in supplying) along with regular free updates and upgrades.
For old hardware (the kind with 1 Core and >500 megs of RAM) there is XFCE or LXDE (+ variants), which are versions optimized for lower capacity computers. If you like the GUI can be made to look like Xp.
For modern, more powerful hardware (2 or more cores, 1 gig plus of RAM) basically there is
Ubuntu developed in the UK by Canonical (owned by millionaire Space Tourist Mark Shuttleworth) featuring Unity --a very modern GUI; from Deutschland there is
openSUSE with KDE and the Plasma GUI producing an integrated set of cross-platform applications designed to run on Linux, FreeBSD, Solaris, Windows, and OSX systems;
Fedora from the USA (formerly known as Red Hat) comes with the GNOME GUI which is very popular in corporate environments.
There are many other variants (such as Linux Mint or Arch) designed to optimize performance at a particular task or environment. They are basically the same cup of joe (derived from Debian, one of the first Linux based OS, first released in 1993) i.e. Fedora, for example, is best known for its security features which makes it popular in corporate networks. For more info I encourage you to watch this documentary, Revolution OS, which relates how GNU/Linux got started, its principles and goals. Two Thumbs UP!
https://www.youtube.com/watch?v=kR6P0GueyVA
If you are not tied to a particular brand of software (Photoshop or Autocad for example, which do not have a Linux version) there is equivalent software packages (for Photoshop the equivalent is GIMP Image Editor and for Autocad there is LibreCAD) that work just as well; there is Open Office, initially developed by Sun Microsystems as an open source (read free) alternative to MS Office, or Laminar Research X-plane instead of MS Flight Simulator (not free but worth it).
Many MS or Apple refuges opt for a dual boot configuration (a PC which allows you to choose between two -or more- OS at startup), as the best of both worlds in case Linux fails to deliver. But as time goes by, these same doubters end up using Linux OS more and more exclusively for their daily computing needs because the Linux OS is so insanely great. Even Apple fanboys renounce their credo once they realize how lame OSX is compared to Linux (and I am one of them).
Your old or new PC will function better, faster and more efficiently with an OS that is not bloated with crapware and vendor lock-in --designed to make you a captive user, and constantly sponging you for more money. Although I advocate the use of GNU/Linux, I understand that this OS has some drawbacks and flaws, and It's not right for everyone. So I suggest you look at it, play with it, consider it, and give yourself a chance to get to know it. If you like it, and it works for you, then use it. If not, then you got an education, and you still come out a winner.