This is the varna compiler for the æternity system which compiles contracts written in varna code to the æternity VM code.
For more information about æternity smart contracts and the varna language see Smart Contracts and the Varna Language.
It is an OTP application written in Erlang and is by default included in the æternity node. However, it can also be included in other systems to compile contracts coded in varna which can then be loaded into the æternity system.