Some time ago I tried Abrechnung and it was quite good actually.

I just set up I hate money a couple weeks ago. Works fine. Not a perfect drop in for splitwise, but works for us. You log in by entering the project name and password (not separate user accounts), then select who paid and for whom.

If you have a nextcloud, cospend is actually pretty good

Kittysplit

Really good one. We were using it to manage our rave organization expenses

UPD oh sorry, you said selfhosted. My bad.

I really like KitchenOwl. It has a lot of features beyond splitting expences, but most can be hidden in the UI.

Its currently in a slightly weird position, as its Github Account was suspended without any explanation. But the app is still available on F-Droid (or PlayStore). They are currently working on the migration to CodeBerg.

But sadly each participant must create an account.

Spreadsheet

I use https://github.com/spliit-app/spliit

It’s not the easiest to self host, as you need to know how to build docker images etc, since none is provided, but it’s more or less a splitwise substitute straight up

Caveats: its completely auth-less, so easy for people to cheat if that would be an issue for some reason. But you also dont have to force anyone to create an account