phpFloodGate allows you to set a rate limit, at which your application can be called, only depending on the time between requests. You have a service you want to offer, but it's fairly wasteful with resources, or you just don't want to take the risk? Just use phpFloodGate.
phpFloodGate uses the Alternative PHP Cache (APC), so you need to make sure that's installed and working.
Licensed under MIT license. See LICENSE for details.