I have gotten to the point that I need to access files from multiple computers.
the only thread I found about this was from 2013.
any suggestions on what free storage options work well ?
one concern is that if I leave a file open on one PC and then go to another, corrupting the file.
I use both windoz and Ubuntu.
You could store your sketches on GITHUB.COM (and that kind alike) for free but than everyone can see (review) them. It gives you instant version control.
for a few $ a month you have private account.
Yes, many people use Dropbox. But yes, you do have to close all the files you have open. Really, how hard is it to close the IDE every time you switch computers?
I use Subversion for exactly this. I have a private repository that's part of my personal website hosting but you can put a Subversion repository onto any PC, so long as it's always switched on and on the internet when you're trying to commit changes from the remote computer.