No, other platforms are not supported.

I think you are mistaken on what is possible on a mt5 netting account, as far as I understand only one common position for a symbol is allowed at a time, therefore the answer is no, only one direction trades at a time with multiple strategy support when logical groups are used in a strategy, no hedging either.

Your assessment would be based on studying the source code?

Do get some ideas on the extensibility. Anyway, I read somewhere that this software does not expire, except after 14 days MT4/MT5 code cannot be exported. but strategies can still be built, is it correct?

Does it support other platforms like MultiCharts, TradeStation etc?

Also, can it handle multiple strategies on same symbol on both long and short on a single netting MT5 account?

There's none! The old legacy one was open-source, but Pro is licensed, so being open would defeat the purpose.

I understand that also read that open source is very old version. But I wanted to assess before buying.

FSB is not the only software other there, there are few others with some having strong focus around robustness.