This article covers the replmon's replacement, repadmin.
While it fails the first part of your request in being a Web/GUI too, it could fairly easily be incorporated into a script that produces html output. (It also produces csv output.)
Do you actively need to actively view the current status? Earlier this year I wrote an Exchange Monitoring script that I published to the http://gallery.technet.microsoft.com/ScriptCenter/en-us. On problems (or certain thresholds exceeded), I have it run as a scheduled task which alerts as needed. (I also duplicated part of it in perl to run from our Linux environment in case a non-fault tolerant part breaks so that the vbs can't alert, the perl/Linux version can.)
I also built a slightly modified version intended to be run manually with reports any problems to the console (instead of email) or simply says "No Issues." (in large friendly letters...)
My point is to ask whether it would be enough simply to be alerted when there's a problem, or if you need something on a screen to look at constantly.
(I can, of course, elaborate as necessary...)