The main Free TON network is main.ton.dev
The main network is available in Surf; however, TON Crystals are not yet available for sale based on a decision made by the Free TON Community.
Devnet runs the latest stable version of the Free TON Blockchain. The goal of the devnet is to provide a stable development environment for application developers. It is optimized to connect with TON Labs SDK. Read more here: https://docs.ton.dev
You can easily switch between the networks in Surf: Settings → Advanced settings → Developer mode.
In Developer mode you can request test Rubies in Surf directly from the Chain Rider bot.
Please note that your Surf address is the same for mainnet and the devnet; however, the address for mainnet cannot be deployed while your TON Crystals balance is zero.