Ignis is the cryptocurrency token developed by the renowned Ardor blockchain. Cryptocurrency pairs including Ignis are listed on the number of exchanges. There is a native exchange Ardor service, where you can buy this asset (as well as NXT and Ardor coins) for fiat and other cryptos.
Bitcoin Gold (BTG) is a Bitcoin hard fork that took place in 2017. The initial goal behind creation of Bitcoin Gold was to increase level of decentralization of Bitcoin network as it became obvious that most of the network is controlled by few mining pools.
OST is currently based on cryptocurrency Ethereum protocol and serves as the currency of the OST ecosystem. The token is represented on the number of exchange platforms paired with other cryptos.