Possibly the only geotagger that works in Linux!
Very simple project, heavily inspired in pictag: you get a list of pictures and a map. Select a location in the map then click "tag" to record the location in your picture's exif data.
Other programs (Pictag, IMGeotagger, Digikam) should be able to do the same but they are either broken, unsupported or use a crappy map. IMGeotaggerV2 uses Google maps and seems to work just fine in Ubuntu 16.04. IMGeotaggerV2 is a copy of IMGeotagger ported for a newer version of CEFPython.
Requirements: pip install cefpython3==56.1
Not tested under other setups. If you do please let me know whether it works.