Each coin or token has a specific problem it aims to solve.

Stellar is an open-source, decentralized protocol for digital currency to fiat currency transfers which allows cross-border transactions between any pair of currencies. - Wikipedia

We offer simple and affordable end-to-end solutions for development, testing and deployment of native C# blockchain applications on the .Net framework. - https://stratisplatform.com

What is IOTA? A permissionless distributed ledger for a new economy - https://www.iota.org

You can go on and on to find what each coin is for.