Other implementations of variant and optional

These are some other implementations of variant and/or optional types. They are not necessarily compatible with this implementation. This is an incomplete list.

• Boost Variant and Boost Optional
• Eggs Variant by Agustín Bergé
• anthonyw/variant (implementation of P0110R0)
• JasonL9000/cppcon14
• tomilov/variant
• akrzemi1/Optional
• mpark/variant