[BBLISA] GPL system monitoring tools? (alternatives to nagios)

[Jeff Ambrosino]

I'm looking for suggestions for any GPL/opensource system monitoring
tools that folks can recommend.

FYI we've been using Nagios for about 6 months now with mixed results.
 While it works, we've had to do an awful lot of customization and
writing our own checks (mostly application-level stuff for our
proprietary software).

I think we would be alot happier with something simpler and more
flexible than Nagios.  Right now it's a choice between further hacking
of Nagios vs. "roll our own" (the latter, I think, will be much more
maintainable over the long run).  But of course I'm looking to avoid
reinventing the wheel as much as possible.

Any feedback or pointers are much appreciated.

thanks,
JB