Options -MultiViews
RewriteEngine on

RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^(\d{4}/\d{2})$ $1.html [L]
RewriteRule ^\d{4}/\d{2}$ render.cgi [L]
RewriteRule ^feed$ feed.cgi [L]

RewriteCond %{REQUEST_FILENAME}.png -f
RewriteRule ^([a-z]+)$ $1.png [L]

RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^([a-z]+)$ $1.html [L]

RewriteRule ^weblog$ weblog.cgi [L]