Sometimes you want to run the same version of a command line program across many operating systems. Maybe your development environment is in Mac OSX and your CI system or production environment is Ubuntu. In these cases you can use Docker to package the command line program into a container which will then be consistent everywhere.
For the past few years, I've used Google Spreadsheets when I wanted to create a small database quickly. Database concepts can be implemented using spreadsheet formulas. Each spreadsheet tab represents a database table; Joins and queries use VLOOKUP (or MATCH/INDEX to optimize); GROUP BY queries are either pivot tables or other formulas. As VLOOKUP count increases, performance goes down, but it's worked reasonably well and Google Spreadsheets is free!
Hosted CI services are becoming more popular. Each service runs your build and tests inside a different operating system with different software pre-installed. If the environment doesn't have the right dependencies installed, you are often encouraged to install them using that CI service's configuration system.
Many free hosted contiuous integration (CI) services exist. These services will automatically compile code, run tests, against
commits or pull requests against your source code repositories, and are
even able to deploy the new code to your production servers if all of the
tests pass. Some offer free builds for open source or public repositories,
giving free compute resources to these projects.