<VirtualHost *:80>
DocumentRoot /var/www/app1
ServerName app1.example.com
</VirtualHost>
<VirtualHost *:80>
DocumentRoot /var/www/example
ServerName example.com
</VirtualHost>
<VirtualHost *:80>
DocumentRoot /var/www/wildcard
ServerName other.example.com
ServerAlias *.example.com
</VirtualHost>
Should work. The first entry will become the default if you don't get an explicit match. So if you had app.otherexample.com point to it, it would be caught be app1.example.com.