Project web site: http://www.saltarelle-compiler.com
The entire project is licensed under the Apache License 2.0, which is a permissive license, so there is no issue using the software in any kind of application, commercial or non-commercial. The reason for this license is that it is the one used in the runtime library (which is licensed by Nikhil Kothari, not me).
To build the compiler and all libraries, open PowerShell, go to the build directory and type
.\psake.ps1. This will generate all outputs in the bin\ directory, of which the .nupkg files are the real artifacts. After running the build script once, you can build both the compiler and the runtime library directly from Visual Studio, but you can't build either from VS until you have run the build script once. Invoking the default task will create auto-incrementing version numbers.
All packages can be installed through NuGet, as well as downloaded from teamcity.codebetter.com.
This project uses the git-flow branching model. This means that all work on future versions should be performed on separate branches forked off of the develop branch. Each commit on the master branch must be tagged with a tag with a name like 'release-version', and will be automatically pushed to NuGet.org.