Updated version of the first ecosystems version. Please post corrections in the comments.
Microsoft, Google and Apple have the most complete ecosystems, with Amazon a distant fourth. The Russian and Chinese markets have their own ecosystems, with Yandex and Baidu dominating. Of course, for most products and services there are also 3rd party (non-ecosystem) competitors as well as open source alternatives.
Update 2019: Microsoft also giving up Cortana and Wallet.