Oh wow. No UPS. There is nothing more satisfying than testing it by yanking the plugs out of the wall, having your UPS start beeping, and then watching your system softly and gently and properly shut down. Plus, with all the time I spent getting my system JUST RIGHT I'm not about to have my file system hosed by something as simple as loss of power.
Anyway I know you want some kind of GUI, but it's not necessary. But if you MUST have a GUI, then just ignore what follows.
I use powerd
http://power.sourceforge.net/
You set it up in your rc.local (or whatever Red Hat uses) to run every time you boot. It's not a big deal
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As an aside, my old, old Dell box USB port was not cooperating with my new UPS, so I couldn't get my UPS to tell my machine to power down. So I dug up an old modem and put it on an open serial port. I then told powerd to monitor the modem. Now, when the modem loses power, powerd notices, and brings the system down after 30 seconds, if the power does not come back on. True, this solution does not monitor the battery level, but it works, and I think it was such a totally cool hack I just have to talk about it at every opportunity
Try doing THAT with a GUI
