Hello There,
I been working on vtiger platform ever since 5.x versions starting from 2008 onwards. I can develop modules, customize existing module, integrate third party API with vtiger, write custom CRON and workflow etc. I have done many complex customizations in vtiger.
I have customized Mail Manager to have multiple email ids i.e one user can use multiple email id in mail manager.
Let me know what kind of customisation you are looking for. I work a lot on upwork and have most Vtiger clients from there.
Looking forward to hear from you
Regards
Ajay