Construct is a single/multiplayer standalone modification allowing the player to build and mold the q1 environment using build tools, pose tools, and effects native to the darkplaces engine.
theres a pretty hefty list of things you can do in construct to all geometry, monsters, even players to a degree. anyone can start a server whether or not you are behind a firewall.
^ you can pose monsters and geometry however you like and use several effects such as scale, alpha, set on fire, auras, additive transparency, positioning, frame toggle, model change, freeze toggle, spawn, and others.
I might have a server up which will come up in the public server list.