Is it's possible to get access to memory that located outside current application? For example I need to check how App2 is using it's memory (check memory fragmentation). afaik every app have own virtual memory, but I need to check memory that located outside it.
Yes, that's how debuggers work, and you can allocate shared memory if the two program will cooperate on it. You can also request access to the raw system memory through the kernel if your program is running with sufficient administrator powers and the system is configured for it.
On Windows, there is a function called ReadProcessMemory that will make a copy for you. On Linux, you can open /proc/[pid]/mem and access it through that. You can also look up tutorials on how to write a debugger and attach to a process that way.
However, I wouldn't attempt this yourself unless you're already experienced... It is so much harder than you realize to get anything useful. Instead, try using existing programs like debuggers and memory analyzers, or instrument your App2 to report on itself.