I've been trying Webmin on FreeBSD, Solaris 8, and HP-UX 11i today. Once I repatriate my AIX box from my employer, I intend to install Webmin on it as well. For FreeBSD, I installed the package provided by the FreeBSD project. For Solaris, I used the package provided by Webmin. For HP-UX, I downloaded the tarball and installed from source. I tried the version packaged by HP with their port of Apache and Tomcat, but couldn't get it to install on its own. Webmin uses its own "miniserv.pl" so Apache is not needed.
Webmin is a Web-based, cross-platform system administration tool. Although I'm not a huge fan of Web-based interfaces, Webmin is slick. I recommend installing the Swelltech theme, which is cleaner than the default.
Using Webmin I successfully installed the lsof package for FreeBSD and Solaris. I didn't have any luck with the same package for HP-UX. Webmin allows you to run commands through the Web browser, so once lsof was installed on FreeBSD and Solairs I ran it and viewed the output in the browser.
One of my favorite aspects of Webmin is its package browsing features. You can peruse the installed software very easily. Webmin also makes browsing logfiles a snap.
Webmin's OS support is vast, since it's written in Perl. I noticed however that not all actions work as well as I'd like. For example, when trying to edit the FreeBSD bootup scripts, I was only given the option of editing /etc/rc.local. I expected to edit /etc/rc.conf or scripts in /usr/local/etc/rc.d. I may have been looking in the wrong place, though.
The two books written about Webmin are both available on the Web for free. The book written by Webmin's author is part of the Bruce Perens Open Source Series and can be downloaded in zipped .pdf. Swelltech's CEO wrote a book and provides it here.
Besides Webmin, there's also Usermin, designed for end-user work. It's good for reading mail. Virtualmin is a virtual hosting management system developed by the Webmin author under contract with Swelltech.