Ethereum is also an open source project. Arguably it's less centralized in this respect than Bitcoin.
Bitcoin is defined by a reference client, which is managed by developers who are mostly employed by a for-profit company. Anyone wanting to do another implementation has to comb through a lot of hairy C++ and match it bug for bug.
Ethereum is defined by a 32-page spec, produced by a nonprofit corporation. At this point there are eight implementations, each in a different language, mostly by entities other than the nonprofit.
Not all cryptocurrencies are alike because there is this fundamental difference in governance. Personally I have a hard time envisioning a successful cryptocoin that does not have a level playing field. The oligopoly of a few companies hiring most Bitcoin developers is problematic, and the Ethereum situation much more so.