You can download this 568k .NET 4.0 executable from Util - Text Based C# REPL v1.0.exe and it should work on your PC and Mac :)
As you can see on the screenshot above, to run in on the mac ou will need to have Mono installed (download it from here) and execute the exe using mono Util\ -\ Text\ Based\ C#\ REPL.exe or mono "Util - Text Based C# REPL.exe" (mono doesn't seem to register the *.exe extension)
Although there is no code-complete (the idea of this REPL is to keep it as simple as possible), a good number of O2 FluentSharp API's seem to be working ok.
For example here is a script that downloads a new DLL (MarkdownSharp.dll) and consumes it
There is also access to .NET's Lamba and Extension Methods: