We sometimes lay out many for a gift with multiple people chipping in. IIUC, I'm supposed to assign the purchase to a gift category and when people pay back, assign those payments as inflow to the gift category. I find that the process has too much friction: I need to keep track of which transactions need to be repaid, and remember to assign the money when it does come in. Does anyone have ideas of how to make the process any simpler?

I don't believe it's correct to assign the whole purchase as a gift category. It should be a split transaction, where the part of it that you are paying for is gift and the rest is accounts receivable. This allows you to track how much money is owed to you in a separate category that should always return back down to 0 once repaid.

So I should have a new category for Accounts Receivable?

Yes everyone should always have an accounts receivable category to keep track of money owed to you. Very common.

I call it "Reimbursement"

Call it whatever! Accounts receivable is accounting words, and that's what I learned in accounting class haha. Reimbursement works haha.

Assuming this question is about YNAB, I also have an Asset tracking account (tracking account means it's off budget) to keep track of how much is owed to me. When I split the transaction (or lend someone money), I set that account as the payee. In a memo I put who the person is and their running total. When they pay back I make it an inflow transaction from that account. All this using the reimbursements/lending money as the category. I wasn't satisfied with only having a category because it wasn't simple to see how much is owed to me at a glance