gksu is described as 'library and application used to ask the user for passwords to run programs as root' and is an app in the Network & Admin category. There are three alternatives to gksu for Linux. The best alternative is ktsuss, which is both free and Open Source. Other great apps like gksu are KdeSudo (Free, Open Source) and x11-ssh-askpass (Free, Open Source).
x11-ssh-askpass is a lightweight passphrase dialog for OpenSSH or other open variants of SSH. In particular, x11-ssh-askpass is useful with the Unix port of OpenSSH by Damien Miller and others, and Damien includes it in his RPM packages of OpenSSH.