The best alternatives to Deskun are Kiwi for Gmail, Zoho Desk, and HelpScout. If these 3 options don't work for you, we've listed a few more alternatives below.
Distinct from what Gmail uses in the browser, we designed a powerful engine that allows multiple accounts to be used together with 100% fidelity and no conflicts. It works with Google Drive, Docs, Sheets, and Slides as well.