Meanwhile the modpack incl. its alio tileset is maintained together with Freeciv below data/alien for data/alien.serv and below data/alio for data/alio.tilespec. The complete modpack (ruleset and tileset) is hosted on modpack.freeciv.org, install it with the modpack installer (2.5 or later). There is also an optional (non-free) alienmusic modpack (2.6 or later).