I don't  really  get your question...
If you mean an exe app that stores testnet btc, there are wallets that allow testnet  btc mode like Electrum and Bitcoin  core .
You can just swithch to testnet mode by launching the exe in a testnet mode,in bitcoin core current installation  using the GUI, the testnet  is also installed along with your standard  bitcoin core separately by default.
If this seem not to be what you meant then elaborate  more......