I have installed a tar package manually. followed the instructions in the readme
Here are the insstructions for installation
load the Qt platform plugin "xcb"
2 1) LINUX
4 First install the following dependencies:
6 -Python 3.5 or later (http://www.python.org)
7 -PyQt 5.6 or later
8 (http://www.riverbankcomputing.co.uk/software/pyqt/download, which boils
9 down to ‘sudo pip3 install PyQt5’).
10 -If you want to be able to enter formulas using latex syntax, make sure
11 that latex and dvipng are installed.
12 -Matplotlib (http://matplotlib.sourceforge.net/)
13 -EasyInstall (http://peak.telecommunity.com/DevCenter/EasyInstall)
14 -cheroot 5 or later (https://pypi.python.org/pypi/Cheroot/,•
15 pip3 install cheroot)
16 -Webob 1.4 or later (http://webob.org)
17 -PIL (https://python-pillow.org, pip3 install pillow)
19 To actually install mnemosyne:
20 -Extraxt the .tar.gz file and change to its root directory (i.e.
21 probably the directory where you found this README file).
22 -Type ‘python3 setup.py install’ as root.
when i run the applicatoin it shows
This application failed to start because it could not find or load the Qt platform plugin “xcb”