Spiro is a spiral-based curve toolkit focussed on type design, and created by Raph Levien. Inkscape, an open-source SVG-based illustration package, of which I am something of a fan, has incorporated Spiro in the most recent release, 0.47. This is pretty exciting, but rather than bore you with details as to why, just check out this video. You will see what I mean.
Source: Typophile