There is nothing put into our XML outputs to stop OpenOffice from working and as far as I am aware the majority of SIMS outputs can be opened by OpenOffice. The exception is graphs in Assessment Manager where we haven't done the extra research to see how to achieve it. We have also made sure that the MS free viewer can be used to stop teachers having to purchase MS Word.
There is a comprehensive third party interface for SIMS and there are a large number of companies using it including Pars. We don't charge for using it to extract data but we do if you start to write data back into SIMS. David Grashoff is the person to contact at Capita.