Linux vendor Red Hat have released a font family named Liberation under a GPL license.
The family consists of three typefaces known as Liberation Serif, Liberation Sans and Liberation Mono each in normal, italic, bold and bold italic variants. The fonts are not hinted in this initial release so may not look too great on-screen at some sizes. Red Hat expect to release better-looking hinted versions in the future. Having attempted hinting Envy Code R font myself they have my sympathy.
These new fonts are designed to be metric-compatible (and therefore interchangeable) with the standard Windows fonts of Times New Roman, Arial and Courier New intending to "Liberate" documents from Microsoft’s fonts. Bearing in mind Office 2007 pushes new typefaces as the default I’m not sure how successful this will be long-term.
Microsoft’s typefaces were designed to be metric-compatible with the classic Times Roman (1931), Helvetica (1957) and Courier (1955) typefaces in the first place so perhaps Red Hat would have been better off licensing or mimicking those instead.
Screen shots follow.
The Liberation fonts on Windows using ClearType alongside the Windows fonts they intend to replace. The free Bitstream Vera family equivalent is also shown (only Vera Sans Mono is metric-compatible).
Microsoft’s Windows fonts alongside Apple’s versions of the originals and the Liberation fonts again all rendered with Mac OS X and sub-pixel precision aliasing. Point sizes have been increased by 3pt to compensate for the difference in on-screen DPI.