The best replacement for collectd is statsd.

The best alternatives to collectd are rated as following:
★★★★★  statsd
★★★★★  munin
★★★★★  ganglia
★★★★  collectl
★★★  zabbix
★★★  sensu
★  cacti

Your alternative for collectd is not listed? Suggest!
Speaking about collectd, one probably shouldn't forget about graphite.

Other search terms related to collectd and their ratings are:
★★★★★ graphite
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Google Trends

Scale is based on the average worldwide traffic of collectd in all years. Click on graph for more.
collectd
statsd
munin