Chax and Smart Crash Reports are Input Managers which are loaded by every Application on your system until they are uninstalled.
They are not Internet Plugins, they are Input Manager Plugins.
Smart Crash Reports has own site which explains better:
http://www.smartcrashreports.com
It comes with Unsanity Applications by default since Unsanity and their fans got nuts about getting APE blamed for every single problem on OS. So, if an APE or SCR enabled Application crashes, crash report is sent to developer too along with Apple. More interestingly, if there is an application enhancer crashing the Application or system, Unsanity and user will hear about it too...
Some people hate them, some don't, I like Smart Crash Reports since I found out Apple does nothing about the crash report and developer can't access his/her own crash report unless he/she works for a billion dollar Adobe or Microsoft.
Oh Chax "enhances" iChat with tabs etc.
Some words you will hear about InputManager issues is not about the insecurity of these plugins or developers, it is the directories default rights which is (really) insecure.