THETA (THETA) coin is the cryptocurrency of the streaming network powering the decentralized video delivery. THETA is listed on multiple Asian exchanges and can be purchased for the South Korean won. THETA can boast solid investors, including Samsung. Being originally an ERC20 token, THETA swapped to its own mainnet in March, 2019.
Tether is a cryptocurrency launched in 2014. It is a so-called stablecoin currently leading by market capitalization. Although according to the initial idea, each Tether was backed by $1 (that was going to keep the price of Tether stable), the company not always managed to maintain this price (at some point in October 2018 the price dropped to $0.9 per one Tether). Tether succeeds in terms of market capitalization and its price is almost all the time is really close to $1.
Scry.info (DDD) is an Ethereum-based token of the Scry.info global data aggregator. DDD token is listed on a few exchanges paired against bitcoin and Ethereum. In this abbreviation, “DDD” stands for "distributed data depositary".