No, there is no demo.  I hemmed and hawed for awhile because I wasn't sure if I wanted to pay for it, but I read enough positive stuff to finally make the jump.  If you are in no rush, there is an expansion coming out soon.  They will probably have a full version packaged with the expansion.  Not sure the eta though.

I also loved playing "Pax Imperia; Eminent Domain". It is a real-time space dominance game. It came out in the late 1990's, so you might even be able to find it on an abandonware site somewhere.

My roommates and I used to play it like mad. It still ahs a couple bugs, but its a really fun, solid game.

homewolrd

homeworld2 - this game is modded like crazy even today

conquest frontier wars (free now via mod)

haegamonia solon heritage

nexus jupiter incident