Part of list:
The Ethereum Lifecycle
To mature the blockchain into a world-class platform for smart contracts and decentralized applications, Ethereum divided its release into four stages, or hard forks, namely Frontier, Homestead, Metropolis and finally Serenity.
It also hard-coded a difficulty bomb, which is a deliberate movement from proof of work to proof of stake. PoS is to be incorporated into these forks through a transition period where Ether would be created using both mining and validation.
This will be achieved by increasing the difficulty of mining from the current 15 seconds upwards, effectively diffusing the difficulty bomb, to a point where it is impossible to discover blocks through mining.
This will be known as the ‘Ice age.’ It is hoped that the majority, if not all of the members of the community will join the forked chain for a more stable, efficient and cheaper blockchain on which world-changing applications can be built.
In Frontier, the minimalist version that launched the Ethereum network was born in 2015. It allowed for uploading contracts, mining, and the availing of ether to exchanges for trading. Decentralized applications could also be uploaded for testing on the EVM.
Homestead has been a beta version of the platform, but it is the one where the network was declared by its users to be stable and safe. In this stage, some of the major projects were started and operated.
Metropolis will see Ethereum reach the street-level user interface milestone. It will be known as Mist, and it will have its dAPP store. Metropolis is supposed to reveal the real power of the Ethereum platform. It will be released in two stages:
The main and final switch in Serenity will be the move from PoW to PoS, achieved through Casper, the algorithm that will enable Proof of Stake as the main means of securing the network. Other changes will mainly focus on making the system faster, easier to use for non-programmers and beginners and also more efficient.