I'd like to point out that it appears their Pipelines is the only hosted CI tool on the market that supports every platform. Are there any others?
There are a bunch of CI tools (Jenkins, Travis, etc.) that offer either hosted service that work everywhere, or on-prem which can be installed on every major platform.
Travis for instance only supports Mac and Linux. Circle CI supports Mac and Linux. Appveyor supports Windows and Linux.
Other tools like Jenkins or Buildkite can be installed anywhere but you have manage the build servers.