Oh falling into the "could built it in a weekend" trap? Go right ahead, start a payroll company from scratch that can correctly pay, with proper auditing, checks and balances, any employee in the US (nevermind international) as quickly as possible, deal with wage garnishments, special deductions (401Ks, IRAs, FSA, HSA, and so on, part-time hourly and full-time salaried, bonuses with net-to-gross and gross-to-net, commissions for sales people along with "draw").... annnnnnnnd go!