I know a ton of people use YNAB (you need a budget), but it is pretty pricy so I've never bought it.
I use an Excel spreadsheet; on the top of the spreadsheet I have a place to input my income for the month. Then below I have all of my budget categories and the amount that I've budgeted for that category each month - the budget categories are nearly the same from month to month but change slightly - sometimes I'll have a vacation line item in there, sometimes a Christmas line item, etc. I have it set up so that each item in the budget category is subtracted from the income category, so below all of these there's a "how much money I have left to budget" cell.
Then to the right of this, I have a column where I can input each purchase I make into the right category, and then next to that I have a column where I have "amount left to spend"; this column is (amount spent-amount budgeted) and shows me, for example, how much grocery money I have left for that month.
I've used this spreadsheet for about 2 years, now, so each month I start a new tab and just copy the cells from last month (so the formulas are all there) and decide on my new budget amounts. This cost me $0 to set up and is really effective for me!