I use a barebones double-entry system (such as GNUCash or Ledger). At the beginning of each month, I set a budget, and I deduct all the forseeable fixed expenses (rent, bills, groceries, eating lunch at work). I also deduct a part for savings and investments. The remainder I divide by the number of days in the month, and that becomes the average amount per day I allow myself to spend on eating out, coffee and other small discretionary purchases. The goal is to have the budget continuosly balance out to zero.

For each of the larger, non-monthly expenditures (travel, quarterly/yearly bills, furniture, electronics) I have virtual accounts in which I put money every month, and take it out when the expense comes, so as to keep the balance of the month at zero. I allow these virtual accounts to go negative, but not often and not for long.

I have a "tab" for shared household expenses; 50% of each shared expense is credited or deducted from the "tab", depending on who paid. This 50% doesn't affect my monthly balance. My partner does his own accounting (i.e. none).

If the months balance is trending positive, I can either increase the daily allocation for the rest of the month, move some to investment, or save more towards a large expenditure.

If the months balance is trending negative, I can decrease the daily allocation for the rest of the month, or save less for future expenditures (which I then have to reduce).

I make the budget of the following month based on what I learned from the previos one(s), and a script that calculates how much money to put into accounts for future expenditures.