Projects lets you tag a variety of transactions, in any category and link them to a specific project.
Add a project by heading to Insights, selecting Projects, and then Add a Project. Once you are all set up, you just get tagging!
Tagging Transactions
When you select either a transaction in your Transaction Inbox or individual transactions within your accounts, you will see your project(s) listed below, select the project you wish to tag the transaction for, and voila!