Tilesets:

perspective_walls.png - (C) Clint Bellanger, released as Public Domain
isometric_grass_and_water.png - (C) Clint Bellanger, released as GPL2, GPL3, CC-BY-SA3
tmw_desert_spacing.png - (C) The Mana World Development Team, GPL
sewer_tileset.png - (C) Blues Brothers RPG developers, GPL
Replica Island - (C) Chris Pruett and Genki Mine, Apache (except hotspots.png)
hexmini.png - Public Domain, http://opengameart.org/content/pixel-hex-tilesets-enhanced
buch-outdoor.png - (C) Michele "Buch" Bucelli, CC-BY 3.0, http://opengameart.org/users/buch
examples/sticker-knight - (C) Ponywolf, CC0, http://opengameart.org/content/sticker-knight-platformer
wangblob.png, CC0, https://opengameart.org/content/seamless-tileset-template-ii