Amplio2 is the default tileset for the GTK client (TBD: and maybe others). Its predecessor Amplio is available as modpack for 2.4 and 2.5. Both versions support isometric (mostly 96×48) tiles suited for isometric topologies. Variants for a hex topology exist, e.g., AmplioHexBig modpacks for 2.4 and later. Actually you could use Amplio2 also for hex. topologies, but of course either the N-S (keypad 8+2) or W-E (keypad 4+6) connections won't work, and 2 of 6 possible hex. river outlets don't exist in tilesets designed for squares instead of hexes.