Tweaking some settings
Set the memcache server
Open app\config\bootstrap.php in a text editor, then search for MEMCACHE_SERVER.
Now replace scratchdb.media.mit.edu by localhost.
Configure Apache to point to app\webroot\
Open C:\XAMPP\APACHE\CONF\httpd.conf in a text editor.
Search for DocumentRoot.
Replace C:/xampp/htdocs by C:/xampp/htdocs/scratchr/app/webroot. Note that it's required to use forwards slashes instead of backwards ones.
Set up a VirtualHost
Open C:\XAMPP\APACHE\CONF\EXTRA\httpd-vhosts.conf in a text editor and add this at the end:
<VirtualHost 127.0.0.1>
ServerName scratch.local
ServerAlias www.scratch.local
DocumentRoot C:/xampp/htdocs/scratchr/app/webroot/
<Directory />
Options -Multiviews +FollowSymLinks
AllowOverride All
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^static/projects/.+/([0-9]+)_(sm|med).png$ static/icons/project/default_$2.jpg [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^static/projects/.+/([0-9]+).sb$ static/misc/default.sb [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^static/icons/gallery/(.*)$ static/icons/gallery/default.jpg [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^static/icons/buddy/([0-9]*)_(sm|med).jpg$ static/icons/buddy/default_$2.jpg [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^static/icons/buddy/([0-9]*)_(sm|med).png$ static/icons/buddy/default_$2.jpg [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?url=$1 [QSA,L]
RewriteRule .*\.svn/.* - [F]
</Directory>
</VirtualHost>
The settings are now configured!