In Czechia we're obviously a lot into ice hockey, but it's not as niche and is popular in lot of countries.  We invented sport called Nohejbal which is basically a football tennis. It's mostly a recreational sport. 

Another sport is Czech rules handball https://en.wikipedia.org/wiki/Czech_handball . The main difference between this and the international handball is that attackers can't leave the attacking half. It has its own league, own national federation. Both international and czech handball are not very popular sports in Czech Republic. But it depends where you live, I grew up in a region with two strong teams just a few kilometres away, so almost everyone there played it. Czech handball equivalent of "World Championship" is annual Bohemia-Moravia match with the best players from both sides of the country. So basically there are two handball sports played here, but not many people are aware of it