MxToolbox has just launched a new Subnet Calculator tool.  It does basic subnet calculations like many online tools, but with an MxToolbox twist.  It also displays a list of each IP in the subnet and automatically does the reverse DNS lookup for you.  Real data, at your fingertips, free for all of our users.

We’ve designed this tool with service providers or larger customers in mind who manage blocks of IP addresses. For our blacklist monitoring customers, we also overlay your blacklist status and reputation data right in top of your subnets. You can also easily save “Name” information directly into the results to make it easier to keep track of things, if your reverse DNS names are not descriptive enough.

All logged in users (free, basic, or pro) will have a history of their subnets available in a drop down menu for easy access.
We are hard at work on more exciting features, and will keep you posted here.