RewriteEngine on

RewriteRule ^/projects/+$                       /projects/index.html [L]
RewriteCond /var/trac/$1                        -d

RewriteRule ^/projects/([[:alnum:]]+)(/?.*)     /projects/trac.cgi$2 {S=1,E=TRAC_ENV:/var/trac/$1]
RewriteRule ^/projects/(.*)                     /projects/index.html