Why the new version is 2.1 while the previous one was 2.90?

Version numbers used by the products on this site are not decimals*: they follow the scheme <version>.<revision>

Thus, 2.10 is not the same as 2.1: the latest MP3 Cat is version 2, revision 10. The previous one was actually 2.9.

* it would be too boring if everyone followed this rule: some people really use them as they were decimals or even marketing tools 🙂 There’s a quite long article on several versioning schemes on Wikipedia for the most curious ones.