Building on Ulrich Palha's comment, I found that this worked for me as an .htaccess file to provide alternative redirects with masking to a couple of my own .php pages:
Options +FollowSymLinks
RewriteEngine on
RewriteBase /
RewriteRule ^(optionOne$|optionOneWithEndingSlash/$|optionTwo$|etCetera/$) ppl/peaceseeker.php [L] [NC]
RewriteRule ^(donny$|donny/$|donnycallahan$|donnycallahan/$) ppl/donnycallahan.php [L] [NC]
(I mention this because Ulrich's solution caused a problem for me when people typed example.com/about/ (with an ending slash)).
Thanks, Ulrich. If anyone knows how to modify Ulrich's .php-suffix Rule to descend recursively into any number of directories, I'd appreciate a comment!
As a temporary solution for anyone who needs to descend into directories, this worked for me:
RewriteRule ^(\w+)$ $1.php [L,NC]
RewriteRule ^(\w+)/(\w+)$ $1/$2.php [L,NC]
The second command will handle the first subdirectory of all directories in the root folder of your website.
You can handle 3 levels of subdirectories, or 4, or 5, or 10, by just adding more instances of "/(\w+)" before the $ (one per new level of subdirectories), and then adding /$3, /$3/$4, /$3/$4/$5, or whatever is necessary immediately before ".php" in the Rule. I only needed 2 levels of directories (for now), so I'm good with what I posted; that solution is simple enough.
I'd still like a recursive solution if possible.