I presume the OP is looking for examples from mathematics. Here is one:

Hadrien De March, Nizar Touzi: Irreducible convex paving for decomposition of multi-dimensional martingale transport plans (submitted February 27, 2017, at 14.23 hours)

Jan Obłój, Pietro Siorpaes: Structure of martingale transports in finite dimensions (submitted February 27, 2017, at 18.52 hours)

The second paper explains:

Finally we note that we have hoped to make this paper publicly available only after having proved Conjecture 1.3. However we have been recently made aware of a parallel and independent work of De March and Touzi who study the same problem and obtain similar results using different techniques. Consequently, we have agreed to simultaneously make our works publicly available.