Is it still opened to join today?

I got a link from Telegram but it was expired or the link was moved to a new one. I guess the campaign already ended. If it is still opened, please help me because I want to join it.

The project looks to be very great with more than $5.2M was secured in Seed phase and many big backers and partners.

I read but not totally understand it. It seems the project is for Bitcoin and Lightning network only. Is it compatible with BSC or Avax?

Both EVM and WASM are Turing-complete, which means that the system can process whatever rule-set of data manipulation, opening up virtually infinite possibilities for developers to create smart contracts. Instead, Mintlayer uses the Bitcoin-like script-based approach: it is non-Turing complete and therefore limited by a determined set of rules that must be followed. This approach sacrifices some versatility in exchange for higher safety, sustainability, and speed of validation.
Generally, script-based smart contracts tend to produce less network pollution and execute faster than Turing-complete contracts, thus ensuring a more manageable environment for developers. On the contrary, complicated architectures on blockchains end up causing more issues than benefits: having endless possibilities might end up clogging servers, while at its core, a Turing-complete system is not even required by most blockchain applications.
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It is one of the main reasons why Solidity smart contracts have shown a higher probability of breaking over time: among the historical failures, more notable ones are the DAO hack and Parity's multiple signature validation program. On the other hand, the possibilities provided by a script-based system are sufficient and proportionate to the purpose of Mintlayer’s DeFi and DEX functionalities, without incurring the risks of Turing completeness. By combining several simple scripts, it is possible to produce highly advanced contracts.