wxHexEditor could open a process memory space at least under Linux.
You need to have enough permissions to do that. (I mean, root)
Devices -> Open Process RAM -> Enter PID -> Click OK
Also you can open the PID with using this command line on start up:
Not that, this feature just for reading.
Writing into process ram is unreliable under current wxHexEditor versions and not advised to use, but free to try.