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How to implement some sort of basic multi-tenancy? For example, to have users with separate data.
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You can implement a multi-tenancy using Jam.py.

For example, if some item have a user_id field, the following code in the 
server module of the item will do the job:

.. code-block:: py

  def on_open(item, params):
      if item.session:
          user_id = item.session['user_info']['user_id']
          if user_id:
              params['__filters'].append(['user_id', item.task.consts.FILTER_EQ, user_id])
  
  def on_apply(item, delta, params, connection):
      if item.session:    
          user_id = item.session['user_info']['user_id']
          if user_id:
              for d in delta:
                  if d.rec_inserted():
                      d.edit()
                      d.user_id.value = user_id
                      d.post()
                  elif d.rec_modified():
                      if d.user_id.old_value != user_id:
                          raise Exception('You are not allowed to change record.')
                  elif d.rec_deleted():
                      if d.user_id.old_value != user_id:
                          raise Exception('You are not allowed to delete record.')                  

It uses a 
:doc:`session </refs/server/abstr_item/at_session>`
attribute of the item to get a unique user id
and 
:doc:`on_open </refs/server/item/on_open>` and
:doc:`on_apply </refs/server/item/on_apply>`
event handlers.

The 
:doc:`on_open </refs/server/item/on_open>`
event handler ensures that the sql select statement that applications generates 
will return only records where the user_id field will be the same as the ID of 
the user that sends the request.

And the 
:doc:`on_apply </refs/server/item/on_apply>`
event handler sets the user_id to the ID of the user that appended or modified 
the records.

You can use a more general approach and add the following code to the server
module of the task. Then a multi-tenancy will be applied to every item that have 
a user_id field:

.. code-block:: py
  
  def on_open(item, params):
      if item.field_by_name('user_id'):    
          if item.session:
              user_id = item.session['user_info']['user_id']
              if user_id:
                  params['__filters'].append(['user_id', item.task.consts.FILTER_EQ, user_id])
  
  def on_apply(item, delta, params, connection):
      if item.field_by_name('user_id'):    
          if item.session:    
              user_id = item.session['user_info']['user_id']
              if user_id:
                  for d in delta:
                      if d.rec_inserted():
                          d.edit()
                          d.user_id.value = user_id
                          d.post()
                      elif d.rec_modified():
                          if d.user_id.old_value != user_id:
                              raise Exception('You are not allowed to change record.')
                      elif d.rec_deleted():
                          if d.user_id.old_value != user_id:
                              raise Exception('You are not allowed to delete record.')