There are train services from Turkey to Bulgaria, Romania, Iran and Austria. 

Only Sofia and Tehran (Transasia) trains run during whole year.

Optima Expres and Bucharest trains run only some periods of year.

The train to Belgrade had run for a short time and then suspended.

The train which is supposed to run on recently opened Baku-Tbilisi-Kars line is annouced to start in August 2019.

Westbound trains

Sofia Express (Sofia Istanbul train)
Plovdiv Edirne train
Bosphor Express (Bucharest Istanbul train)
Belgrade Istanbul train
Optima Express (Edirne Villach train)

Eastbound trains

Transasia Express (Ankara Tehran train)
Tehran Van train
Van Tabriz train