Open Source Tax Software
The IRS option Free File Fillable Forms has online forms that compute internal arithmetic and self-efile. This eliminates many hand math errors.<p>However this system isnt good at telling you which forms you need to file. You could miss an important one. For example sometimes you need a Schedule D and sometimes you dont. If you income reaches six figures you have to calculate the AMT and NIT forms to see whether they apply or not.