Schema comparison tools for ACA file validation

Wondering what tool people use to validate their ACA files against the IRS schema. I used a trial copy of Altova XMLSpy last year and it worked really well. But, I'd like to find a free software. What other tools do you have experience using and are they user friendly?

@Evelyn Bian
Thanks for sharing Evelyn. I will have to inform our developer about Visual Studio as an alternative to Altova. We do have to renew the Altova license so maybe we can have another alternative before the renewal.

@Tricia Smiley We were able to get Visual Studio to work. A developer on our team uses the tool regularly but was having trouble getting it to produce results that made any sense. It wasn't until he downloaded a trial version of Altova XMLSpy and compared the results between Altova and Visual Studio did he figure out how he needed to configure Visual Studio to do what it needs to do.

@Evelyn Bian Our agency tried NotePad ++ last year but found success in using the trial version of Altova XMLSpy last year. A license for Altova XMLSpy was purchased for this year. It would be interesting to know if there are other tools that are better than XMLSpy.