Kayako
Kayako is the leading help desk 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 integrate Kayako software with WHMCS, simply take a look at the /integrate/ folder of your SupportSuite or eSupport download (available from the Kayako members' area) package for the files and instructions.
If the /integrate/ folder and its files are not present, contact Kayako support and they should be able to provide you with the files you need.
Once you have edited and uploaded the files as described by the readme document found in the /integrate/ folder, you will need to activate the integration within WHMCS. Simply log into your admin area and go to General Settings -> Support and choose Kayako from the Support Module dropdown menu.