Sumokoin is a fork of Monero by four developers who actively work on this coin since half 2017 and have reached their roadmap milestones so far. Mobile wallet follows in Q1 2018. Sumokoin implements a few features that make it better than Monero on various fronts. Better privacy, better wallet GUI and other specifics make it a good sister of Monero. There is no competition with Monero; the Devs share their knowledge with Monero Devs. The vision is being the best privacy coin.
Small as it still is, an excellent growth coin.