We don't have any MS-Windows clients. The GUI must be Linux-based (this includes a web-based system accessed via a standard web browser).
Under Linux, Luma http://luma.sourceforge.net/
You can also manage your directory with a browser using the following (among others):
phpLDAPadmin http://phpldapadmin.sourceforge.net/wiki/index.php/Main_Page
LDAP Account Manager http://lam.sourceforge.net/
Webmin (general system administration, including LDAP) http://www.webmin.com
The answer is already in my post. I use all of them, according to circumstance and specific need.