<title>{% get_fragment request "frag_title" %}</title>
{% fragment request "frag_title" %} my title {% endfragment %}
Thank you Martin! Your solution worked for me.
But I edited it a litte bit for my needs so it will work with FeinCMS page modules.
If someone searches for similar problem, here is how I made it:
3rd app template:
{% fragment request "title" %} my title {% endfragment %}
base.html:
{% if request|has_fragment:"title" %}
<title>{% get_fragment request "title" %}</title>
{% else %}
<title>{{ feincms_page.title }}</title>
{% endif %}