It used to be a tradition that there would be a big mass release of unused or unpopular WWE talent every year almost immediately following WrestleMania. In the past couple years, however, the company has opted to simply let talent contracts expire and "release" Superstars via not renewing contracts, partly because of the sunk cost of the contract payout and in part to avoid hard feelings.
A handful of contracts appear to have been up on Thursday, because the WWE suddenly announced the release of ten individuals (so far).
UPDATE: JTG has also been released. Formerly a member of Cryme Tyme, JTG hasn't appeared on WWE programming since a loss on "Superstars" in September 2013.
Drew McIntyre, who was last seen as part of the cult-favorite 3MB and was at one point in the storyline Vince McMahon's "Chosen One" and former Intercontinental Champion. He was also troubled by some out-of-the-ring issues during his early days in the company.
Jinder Mahal, another member of 3MB. Although Heath Slater has not been released (as of yet), 3MB is officially dead.
Aksana, who was just on RAW, getting beat up by former tag team partner Alicia Fox. The Lithuanian is a former fitness model and bodybuilder who had an awesome theme song with porno sax in it.
Curt Hawkins, former "Edge Head" and longtime tag team partner of Zack Ryder.
Theodore "Teddy" Long, former manager, general manager and creator of impromptu tag team matches.
Camacho, former tag team partner of Hunico (who is now Sin Cara), last seen on NXT feuding with Adam Rose.
Brodus Clay, formerly of one of the most unfortunate WrestleMania moments in history, former member of Tons of Funk and last seen on NXT in a championship feud with Adrian Neville.
Evan Bourne, who had actually been off television for two entire years of his six-year run due to injuries. The former Matt Sydal on the indies will likely head back to ROH and Dragon Gate USA and be a big deal there as the returning hero.
Yoshi Tatsu, who allegedly once beat up Sheamus after Sheamus threw a protein shaker at him. Tatsu will likely head to NJPW or another Japanese promotion, if he doesn't do an indie tour of the U.S. first.
And for pure speculation, these are the Superstars I would imagine are on the endangered species list and/or currently have their phones turned off: Justin Gabriel, David Otunga and perhaps even Zack Ryder or Heath Slater (although the release of Slater would allow for the reunion of 3MB on the indies, which wouldn't be the worst thing ever).