Delta Patcher is yet another frontend to the xdelta3 decoder/encoder created by Joshua McDonald. Delta patcher is able to make and apply patches. But... why making another frontend? All the frontends I've seen don't support some options of the encoder/decoder at all, like compression level for encoding and checksum checking for decoding/encoding. Also, they are all written in .NET (0_0). So, this tool was designed to be selfcontained (as of now, only for Windows). It's written in C++ using wxWidgets for the GUI components and all the needed libraries are static linked to the EXE. All you need is to place the xdelta.exe file in the same directory of this tool (no more .NET Framework required). Last, but not the least, Delta Patcher is GPL2'd and cross-platform: it runs fine on Windows and Linux and should compile on MacOS too.
This package comes with two versions of the frontend. The Lite version is simply the patching GUI, this is intended to be shipped along with your patch. This way, the final user doesn't need to mess with other options like patch creation (simplicity comes first!). The Full version is mainly for romhackers, it supports both creation and application of xdelta patches.