gistfile1.py

## common/models.py
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class CommonFile(models.Model):
    """ Model for common files. """
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    order = PositionField(unique_for_field='object_id')
    title = models.CharField(max_length=255)
    title.alphabetic_filter = True
    description = models.TextField(null=True, blank=True)
    upload = models.FileField(upload_to="uploads/files/")

    def __unicode__(self):
        return self.title

    class Meta:
        verbose_name = "File"
        verbose_name_plural = "Files"
        ordering = ['order',]

## common/admin.py
from django.contrib.contenttypes import generic

class FileInline(generic.GenericStackedInline):
    model = CommonFile
    allow_add = True

## other_app/admin.py
from common.admin import FileInline

class OtherModelAdmin(admin.ModelAdmin):
    inlines = [FileInline,]

## other_app/models.py
from django.contrib.contenttypes import generic
from common.models import CommonFile

class OtherModel(models.Model):
    files = generic.GenericRelation(CommonFile)