[Theo's question][1] made me wonder if there are other "noncommutative analogs" outside of operator algebras. Some noncommutative analogs from operator algebras include:

 - A $C^\ast$-[algebra][2] is a noncommutative [topological space][3] (cf. the [Gelfand transform][4]).
 - The [multiplier algebra][5] of a nonunital $C^\ast$-algebra is the noncommutative [Stone-Cech compactification][6].
 - A [spectral triple][7] is a noncommutative [manifold][8] (add some extra data to the spectral triple to get a noncommutative [Riemannian manifold][9] cf. arXiv:0810.2088).
 - A [von Neumann algebra][10] is a noncommutative [measure space][11].

Are there any other good examples? If you know more in operator algebras, that's great too.


  [1]: http://mathoverflow.net/questions/7095/which-is-the-correct-ring-of-functions-for-a-topological-space
  [2]: http://en.wikipedia.org/wiki/C*-algebra
  [3]: http://en.wikipedia.org/wiki/Topological_space
  [4]: http://en.wikipedia.org/wiki/Gelfand_transform
  [5]: http://en.wikipedia.org/wiki/Multiplier_algebra
  [6]: http://en.wikipedia.org/wiki/Stone–Čech_compactification
  [7]: http://en.wikipedia.org/wiki/Spectral_triple
  [8]: http://en.wikipedia.org/wiki/Manifold
  [9]: http://en.wikipedia.org/wiki/Riemannian_manifold
  [10]: http://en.wikipedia.org/wiki/Von_Neumann_algebra
  [11]: http://en.wikipedia.org/wiki/Measure_space