YNAB. It works well, and they added in the ability to use Google accounts to log in. So I added my wife not by sharing the username/password, but by logging in on her computer once, and adding her Google account.

If you want simple, it is that. My only issue is the inability to have multiple currencies as my wife is from Argentina and I'd like to, more easily, track assets in both USD and ARS. Right now that requires a manual conversion (but the rate is unstable) or using two budgets (the approach I've used) which is tedious, but we don't do much with ARS so it's not a real hurdle.