It's a good month to be a fan of quirky puzzle games if you're a PlayStation Plus member. Just in case last week's addition of Resident Evil 5 wasn't quite your style, this week's addition is a bit more cerebral: Quantum Conundrum for free.

Quantum Conundrum becomes the latest piece of the "Instant Game Collection" tomorrow. In addition, PlayStation.Blog tells us members can also get a 30% discount on Machinarium, bringing its price down to $6.99 instead of the usual $9.99.

Both games are well-received by critics. Quantum Conundrum gained notoriety from its association with Kim Swift, one of the creators of Portal. Its first-person platforming puzzles bore more than a passing resemblance to Valve's hit. Machinarium is more of an indie darling, notable particularly for its art style.