Sure but truth be told, Mono is not as good as the official .NET Framework, even more so when it comes to doing GUI applications. I don't think most people would choose Mono to do a serious cross platform application, when Qt and Java are so much better for this.
That's exactly the point I was trying to raise--without an integrated framework (like JRE), it's hard to consider Mono and .NET as a cross-platform toolkit. In fact, .NET and Mono have entirely different APIs to do UI, while Java is more/less integrated with respect to different JREs (including OpenJDK, Oracle, IBM, etc).
People have tried really hard to bring C# on to other platforms even when it starts feeling forced.
Sure but truth be told, Mono is not as good as the official .NET Framework, even more so when it comes to doing GUI applications. I don't think most people would choose Mono to do a serious cross platform application, when Qt and Java are so much better for this.