Custodian is a lightweight resource monitor that makes it really easy to sample metrics and display them anywhere.

Start Custodian and configure it to sample metrics every 60 seconds and expose them over HTTP on port 5100:

$ custodian start --port=5100 --interval=60

Custodian aggregates statistics from samplers, and ships with samplers for popular metrics such as CPU, RAM and disk usage.

$ custodian samplers
15 compatible samplers:

cpu         CPU statistics
ram         RAM statistics
disk        Disk statistics
...

Samplers are just simple Ruby classes:

class Who < Custodian::Samplers::Sampler
  describe "Logged in users"

  def sample
    `who`.lines.collect { |line| line.split.first }
  end

end

You can load your own samplers with the --samplers option:

$ custodian start --samplers=~/.custodian/samplers

Unless you're crazy about JSON, you'll probably want to consume Custodian's API with a client. Unfortunately, there are no clients for Custodian yet — you should make one!