I used WebHelpDesk for years. Great product. Easy to customize, excellent GUI. Less integration capabilities then other systems (like ZenDesk), and a bit pricey, but really does the job.
I've used Asana for project management tasks with school districts, charters, and vendors. Great product and it keeps getting better. Reasonably priced, including free version to try out for 5 or less users.
It's easy to back a product when you believe in it 100% Teachers win, students win! If you are an educator, you have to check this out! https://youtu.be/v4_B7nHeqVc