Sounds like Munin would suffice for you. Also, it's free.
munin-monitoring.org
> not really that good
New relic has such rich functionality that it is easy to overlook some of its utility. It took us a while to get it tuned to our needs, but now that we have it configured, I couldn't imagine running a high availabilty web service with anything else. Suppose I get a pagerduty for high memory usage on a server. I would then go look at that server in new relic, see what processes are using the memory, see what the memory usage for that process has been like for the last 6 months, perhaps notice a slow steady increase in memory consumption, realize there's a memory leak, etc.
And I've been getting way too may false positives on the systems alerts.
If you only want systems monitoring and not deep application performance insight, New Relic is way too pricey and not really that good.