Everything and that is why I'm terrible. I should just stick with one language and get good at it. The curation specialists are Ruby. Alot of the tools on site are JS, The Website is HTML, CSS, PHP, and JS. All Ethereum Stuff is Solidity. I'm going to start looking at EOS and see how they are planning on allowing apps to build on top of it. If they have docs and it is in a normal language that everyone can use then I would suggest everyone Learn that language who is interested in blockchain development as EOS does appear to be the latest and greatest blockchain development since Steem.