Does anybody know are there free C library that implements most features of C++ standard library?
e.g. I've used Berkeley in-memory db as maps (hash) but this isn't sufficient

What features?

For hashing how about the GP hash function library?
http://www.partow.net/programming/hashfunctions/#top

Another choice is to use perlcall to create a callback to access perl library calls:
http://www.xav.com/perl/lib/Pod/perlcall.html

Thanks in advance
But I think this thread is far from closing...
Any other suggestions are welcome

Gut,
but what about std algorithms (e.g. find, sort, etc.)

For sorting arrays in C, you can use qsort, see 'man 3 qsort'.

If you need abstract streaming types, investigate libSDL, it has neat things they call SDL_RWops. They're structures full of function pointers that can be populated by any functions you want. SDL comes with ones for reading from files and memory, and I've written an extension library, SDL_rwlib, that includes things like TCP/IP sockets, UNIX fd's, gz streams, bzip2 streams, temp files and temp memory spaces, ring buffers, and an SDL_rwprintf.

What else do you need? If you're looking for a total replacement of C++ STL, you're out of luck, since the closest thing C has to templates is macros...

the glibc has hash functions, several others have more specialised functions.
can you please explain what problem you try to solve with those hashes. it will be easier to usccest an alternative solution

I've found something interesting for hash: http://www.cl.cam.ac.uk/~cwc22/hashtable/