This is a downloadable sim that costs $29.99 for a 255mb download from Thirdwire. The sim is classed as a "lite" sim which means you will be able to run it well on older computers without having to pay for expensive upgrades. First Eagles has had fair success in the PC games market, although its impact has a lot to do with the game having an 'open architecture' allowing others to modify and improve aspects of it and add new planes, terrain, weapons etc. There are lots of very good quality downloads available from several sources and an active user support base.
This sim is one that I would always have on my netbook for when I go travelling. You can download some photoreal sceneries for it, and in its latest incarnation available from Quality Simulations it is a sailing/flying/gliding/driving sim. This VSF version is free as it is a beta version. Microflight 5.0 and Virtual Sailor are both available as downloads from the site for $30 each. They do not take up many resources and there is a selection of user created ships, sceneries, planes and other vehicles that will be guaranteed to appeal to everyone. On my last vacation I flew from my home in Adelaide, South Australia to California, and visited places such as the Grand Canyon, Las Vegas and San Francisco before getting on board the Celebrity Infinity for trip down the Mexican Riviera and through the Panama Canal to Fort Lauderdale. I flew the Grand Canyon, San Francisco, and Panama and also transitted the canal by cruise ship before I ever got there using Microflight and Virtual Sailor!
One sim causing a lot of interest is Rise of Flight. This title from Russia has some of the best graphics ever seen in a sim. For more information visit their website at Rise of Flight.
If you have FS2004 or FSX then you can experience the joys of flying those old WWI machines by buying WWI Dogfight from Abacus Publications. I ordered that title plus Battle for Zeebrugge and Day of the Zeppelins from them for a total cost of $36 US in one of their regular sales. The missions only work in FSX but the visuals are pretty good with the exception of the propellor disk that looks bad on my PC. As always, MSFS graphics are awesome but resource hungry. You get a Sopwith Pup, An Avro 504, a Nieuport 17, a Fokker DR-1 and a Zeppelin to play with.
If you have either of these titles it is possible to use them as WWI sims. With CFS2, you do this by downloading new user created menu screens and planes from sources such as those listed on the resource page. The big advantage to using this sims is that it has been around for a long time and there are no new commands to master. Most modders have figured out all of the tweaks and tricks that can be used to get the most out of it. All of the many fine add ons for CFS2 are free as well, you just need to buy a copy of the original program CFS2.