At the National Theatre we used Jira and am just looking to implement that here.
At National we used it to capture customer issues partuicularly web ones, but also for requesting offers and new events to be set up, for merging customers and households, data requests and customisations as well as workflows for processing Gift Aid and some of the newer tasks we had to do when we launched the web site.
It is free for non-profitshttps://www.atlassian.com/software/views/community-license-request
Although it was designed as an Agile Project management system they have added a Core product which is essentially just workflows.
They also do a Service Desk product too which is really useful as uses the same workflows but gives you an interface that allows you to prompt the user as to what to enter where for different types of activiity.
There is also a marketplace with add ons (most of which you get free in the community licence) which allows you further customise and automate the workflows.
Plus you can then couple it with Confluence whcih gives you a great place top store and organise documentation and can also act as a knowledgebase for the Jira Service Desk.
You can also with Confluence and on Confluence Questions which allows any user to submit a question then others to answer it and vote on the best answer. If this is a new Tessitura installation it may be a nice way of encouraging people to get more involved in Tessiitura by asking questions and for others to show what they have learnt.
Mark