I found an instant diptych maker called DipStych, for old-fashioned people like me — who still use Windows* & don’t have an iPhone**. This took about ten seconds to make. It’s also got an easy way to quickly add a border to your photos without having to open up PS (see below).
*There isn’t a Mac version.
**I’m envious of your apps but I like my $100/year cell phone bill more, I think.