data = {'Author1': defaultdict(<class 'dict'>,
                        {'Microsoft': 248,
                         'Ubuntu': 24,
                         'IOS': 24,
                         'Solaris': 24,
                         'C': 248}),
 'Author2': defaultdict(<class 'dict'>,
                           {'Microsoft': 38,
                            'Ubuntu': 38,
                            'IOS': 38,
                            'Go': 38,
                            'C': 38}),
 'Author3': defaultdict(<class 'dict'>,
                    {'Microsoft': 2,
                     'IOS': 2,
                     'Go': 2,
                     'C': 2})}

Name       Microsoft  Ubuntu IOS Go Solaris C
Author1       248        24   24  0   24     248
Author2        38        38    38 38   0      38
Author3        2         0     2  2    0      2

html = '<table><tr><th>' + '</th><th>'.join(data.keys()) + '</th></tr>'

for row in zip(*data.values()):
    html += '<tr><td>' + '</td><td>'.join(row) + '</td></tr>'

html += '</table>'

print(html)