Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
Glade - Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit...
Mailwasher - Over 8 million people use MailWasher as their spam filter
wxFormBuilder - wxWidgets is an excellent framework that enables the creation of multi-platform applications with...
SpamAssassin - Use this program to "Unspam" your mailbox(es).