Before GFWL or Steamworks set up shop, GameSpy ruled the PC multiplayer roost as it integrated into many games; from GameSpy Arcade to GameSpy Comrade.
As of May 31st no GameSpy-dependent multiplayer will function and that's bad news for older desktops. Bohemia Interactive is so far the only studio to take action.
They've got plans in the works to help Arma 2: Operation Arrowhead and Arm 3 users switch to using Steam instead, but their other titles (Take On Helicopters, Arma 2, Arma 2: Free, Arma, Arma: Cold War Assault) "will have more limited multiplayer experience with loss of server browser, cd key authentication and NAT traversal systems," they said.
There's still the direct IP connection route though, suggests Bohemia.
In its prime, GameSpy Arcade handled the likes of EA's Medal of Honor and C&C Renegade, but over the years it lost prominence as others starting muscling in. Eventually the likes of Steamworks and Games for Windows Live all but killed it. GameSpy Technologies was bought by Glu Mobile in 2012 from previous owner IGN.
Given how far back some of these games stretch not many will survive online in this post-GameSpy world. Games for Windows Live is much more recent but there's still going to be casualties when Microsoft switches it off.
...on the plus side, no GFWL or GameSpy Comrade clients to bend over for. Silver linings matter.