Estonia, Latvia, Lithuania, Georgia and any other country threatened by a large invasion prone neighbor should pool money for a annual open source weapons design contest. I would envision at least two separate categories: one for helicopters and one for armored vehicles. Both contests would offer a series of prizes for best designed and deployed systems. The problems are stated and no other constraints are given. Any team can approach the problem any way.
All current MANPAD and personal anti-armor weapons systems are the products of bloated defense establishments and legacy thinking going back to the dawn of the computer age. Today's world offers the tools for any technically inclined individual to design and build a usable system.
All entries must be completely open source so that in the second iteration of the contest any team can use any aspect of another teams previous entry. This will ensure maximum innovation each year.
The winning systems should not even go into production nor should any attempt be made to prevent potential adversaries from knowing the details. The plethora of possible threats upon any invasion will prohibit any usable defense.
If any government chooses to use the intellectual gains of such contests, they would best do so merely by stocking throughout their country the commercial off the shelf (COTS) parts so that in the event of an invasion partisans can assemble weapons systems as best fits their needs on the ground.