TaxGeek is a Mozilla-based US income tax program that includes Form 1040, Schedules A, B, C, C-EZ, D, E, K-1 (1065), SE (Short and Long), W2, Form 8880, Form 8863, and Form 2441 with access to most other files as PDFs.
itax is a free/open source multi-platform implementation and extension of the Australian Tax Offices(ATO) 'e-tax' software.
phase 1 of this to create a free/open source multi-platform implementation of the ATOs e-tax
phase 2 is to extend e-tax