where can I find an overview of the technologies that blockchain startups use?
Are most ICOs based on Ethereum's Solidity Smart Contracts, creating a simple ERC20-compatible token?
Why are the alternatives like Hyperledger, Chain, Bitstake not so common?
At the writing of this TokenMarket lists 493 token projects for Ethereum. This is from total 720 projects. Thus, it can be said most token projects are on the top of Ethereum.