A simple C# CLI program that takes in your Terraria .plr file, and prints out a list of items you haven't researched yet. It relies on the Terraria Wiki for an up to date item list; on the off chance that Terraria gets a new release, it may take some time for the wiki to be accurate to ther latest game version. Otherwise, this list should only contain items that are actually researchable by the player.
To compile, you'll need Visual Studio and .NET Core. Just point VS to the .sln file and it should know what to do.
VS Code is also an option here.