There's a lot of custom cursors for Linux-based distros on sites like Opendesktop / "pling" or Deviantart.
The following instructions are for distros using Gnome desktop.
First, make sure you've extracted the theme and inside the theme-name folder, a cursor.theme file exists, in the following format:
[Icon Theme]
Name=nameoftheme
Then, put the theme somewhere, I added themename
to ~/.local/share/icons
As sudo or root, run the following (adjust path/filename of themename to suit):
update-alternatives --install /usr/share/icons/default/index.theme x-cursor-theme /home/angela/.local/share/icons/themename/cursor.theme 10
Run update-alternatives again, to show a list of available cursor themes:
update-alternatives --config x-cursor-theme
You'll be shown a list of themes you can pick from, type the corresponding number of the theme you want to use:
There are 2 choices for the alternative x-cursor-theme (providing /usr/share/icons/default/index.theme).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/share/icons/Adwaita/cursor.theme 90 auto mode
* 1 /home/angela/.local/share/icons/themename/cursor.theme 10 manual mode
Press <enter> to keep the current choice[*], or type selection number:
ALT + F2
and in the prompt, type r
to restart Gnome shell (if using a laptop keyboard, try CNTRL + ALT + F2)