RainCaptcha provides anti-spam protection in the form of a CAPTCHA test. The distorted text the test produces is designed to be easy for people to read, but hard for machines to decipher. RainCaptcha requires no registration and is free for both personal and commercial use. It works on any web server and is easy to implement thanks to its reliance on APIs for integration.
The following is a list of SDKs from our SDK directory that matched your search term. Though your definition of an SDK may differ, in our world, we define SDKs as platform- specific tools for consuming existing APIs of the sort we list in our API directory. For example, the Ruby SDK for consuming the Twitter Ads API. If you think an SDK, API, or other asset is missing from our directory, be sure to check our guidelines for making contributions to ProgrammableWeb.