ETCDEV have been maintaining and improving Geth since the fork, and are going to continue this work with a focus on architecture modularization, performance improvements and making it friendlier for using in the business environment. Classic Geth is a fork of ETH Geth, but developed separately since October 2016 (up to 50% of the current code has been rewritten/replaced/removed).
Mantis is a node client built entirely from scratch using Scala. Scala is a programming language that supports functional programming and favors immutability. It also offers developers ease of testing and predictability. The client is also compatible with the Daedalus Wallet, which provides users with a UI to access and manage funds. Mantis sets the foundation for future innovations in Ethereum Classic.
SputnikVM is a highly efficient and pluggable implementation of the Ethereum Virtual Machine. It is a standalone EVM that can operate independently of a blockchain and is capable of running on low powered devices; with plans to run on ultra-low power devices.
Sidechains will become a native part of ETC infrastructure and protocols. This will increase ETC’s scalability and bring blockchain to a diverse group of handheld and IoT devices for the first time.