Kayako
Kayako is the leading support suite software for businesses with multiple team members and teamwork/assignment requirements. WHMCS now allows you to combine the best of billing with the best of support should your support needs outgrow that of the built in functionality.
To install Kayako into WHMCS, simply take a look at the /integrate/ folder of your SupportSuite or eSupport package for the files and instructions. If these files are not present you will need to contact Kayako support and they should be able to provide you with the files you need.
Once you have edited and uploaded the files required by Kayako as instructed, to activate it within WHMCS, simply login to your admin area and go to General Settings > Support and choose Kayako from the Support Module dropdown menu.