Carbon is an open source PowerShell module used to automate the installation and configuration of Windows servers and Windows applications. It has been downloaded over 15,000 times
Blade is an open source, NUnit-inspired testing PowerShell module for testing PowerShell modules, functions, and scripts. It is used by the Carbon, PsHg, and Rivet projects. I wrote it before I knew about Pester. Now I have so many tests that it would be burdensome to switch.
Rivet is an open source, SQL Server database migration tool. Database changes are scripted using PowerShell. Inspired by Ruby on Rails' migrations.