Puede hacer esto con una subconsulta correlacionada:
select a.*,
(select application_stage
from application_progress ap
where ap.application_id = a.id
order by stage_date desc
limit 1
) MostRecentStage
from applications a;
EDITAR:
Puede unir los datos del solicitante con algo como esto::
select a.*, aa.*,
(select application_stage
from application_progress ap
where ap.application_id = a.id
order by stage_date desc
limit 1
) MostRecentStage
from applications a join
applicant aa
on a.applicant_id = aa.id;