Questions about RS-232-like naming and standards
(disclaimer: this is from memory, it was 15y ago that I had to study these standards.)

Contrary to what most people seem to think the RS-232 and similar standards describe only the electrical aspects, and at a very crude level the function of the handshake lines. The data format is NOT described in these standards.

=== 1 Is official RS-232 (EIA-232) standard open and free available?

No, it is not free. (Note that there are three: RS, TIA/EIA, and CCITT/ITA.)

=== 2 Does "RS-232 with TTL levels" is covered by some standard?

No. That would leave only the data format aspect, which was not in the standards in the first place. 

=== 3 Does "synchronous RS-232" (via USART) is covered by some standard?

I assume you mean data transfer accompanied by a synchronous clock? I don't recall, because that was not what I was after when I read the standards. I vaguely recall that there is provision for a clock line, but not even a mentioning of the clock level on which the new bit should be shifted out.

=== 4 Is there general name for RS-232-like protocols with different voltage levels?

I assume you mean the asynchronous serial data format? The fancy name for that is non-return-zero start-stop. non-retrun-zero (NRZ) means simply that a 0 is tranmitted as one level and a 1 as another level, without any extra edges inserted or removed (as for instance Machester or NRZI would do). start-stop means that a start bit (polarity oppisite to the idle polarity) is prepended, and a stop bit (polarity same as idle polarity) is appended.

I always found it strange that a 'standard' that is used so widely is not standardised. But when I tried to find the standard description of SPI I found the same situation.