Some friends and I have been playing a browser based game called SKAPH for about two months now. (Of course the initial attraction was the giant robots angle.) This is created by a German company, and it shows a bit in the translations to English, but the basics of the game are not too hard to figure out.
Battling robots are always nice, but SKAPH is really a game about resources and building. Your base starts with limited resources (you have crash landed on an alien planet) and you must construct mines and factories to create more, plus conduct reseach for new technology and structures. Building construction and resource accumulation is slow, paced so that players can play for a few minutes 2 or 3 times a day. Getting my first base up and running took over a week, but the construction times for basic building have since been radically reduced to help get new players into the game more quickly.
Once you get your base established, you construct a Map Room, at which point you are placed into the harsh world where others can attack you (all the other players crash landed too). Attacks become stronger as players bases grow, and alien attackers soon join the battles too. Damage is easily repaired, but your base will require regular attention. If you are persistent, your base will keep growing even when subjected to regular attacks. The only real way to lose is not to play; your base will be destroyed as multiple attacks strip away defenses and your headquarters is finally destroyed. (Caution: Attacks can be much more serious if you start on "hard", and a player in my group recently restarted to escape an unplayable starting location, surrounded by unhappy aliens.
Manage your resources well, make a few allies among your neighbors, and you will prosper. The majority of players n the game are German, but most know enough English that I can make deals with them (and there is always Google Translate, but the Germans maylaugh at you.). If you start on the "easy" difficulty level, you will be placed among other new players, and any attacks made on you won't be too harsh. Of greater concern is the resources that are stolen from you in attacks, and you will want to build defenses for protection from raiders.
There is a commercial aspect to this game, mostly in the form of ads. Additionally, your base is powered by Reactors with limited supply, and for a fee you can purchase Uranium to feed nuclear reactors, supplying greater power and making your base more efficient. Nuclear powered robots and weapons can eventually be built, but I have not progressed far enough yet to see this. The game is quite playable without spending any money on it.
And playable is the word for it. The pacing is slow, and the development of your base is spread out over weeks. This might seem frustrating, but there is a lot of satisfaction in seeing the game unfold and the difficulties encountered along the way. The game has stayed interesting for me all the while, and I'm looking forward to the next stage of research, so I start building the advanced combat units.
There are some nice animated promos too. I can't embed Flash here, but here are some links to the movies.
I could say more about actual play, and offer some tips, but part of the fun is figuring the game out for yourself. I'm open to answering question though if someone wants help.
Finally, here is a screen capture of my primary base, the green bars indicate some damage I have not repaired yet, and my current resources along the top. The in-game graphics are not so nice as the demo material, but are still effective and nicely done.
--- UPDATE: More about Skaph ---