Last week, PowerShell.org created a hosted TeamCity instance which is free to use for any open-source project.  What sets this apart from other similar CI solutions out there is that we're customizing build agents and project templates specifically for PowerShell script / module testing.  If you're hosting an open-source PS project on GitHub, and you're already using Pester for testing, then the effort involved to get your project set up is virtually nothing.  The template used to create new projects will automatically run your Pester tests against every commit (including pull requests), on PowerShell v2 through v5, and publish a pass or fail status back to GitHub.

http://powershell.org/wp/community-build-server/ for more information.