For developers of games on XNA, there are quite a few useful and not very projects that will make life much easier and will save you from writing your bikes. Here is a small list of suitable open source projects for xna:
RamGec XNA Controls
This project is a very easy and convenient GUI in Aqua (like a Poppy) style, easy to implement and understand, but average in functionality.
Pros:
1) Excellent documentation
2) Ability to change skins
3) Open source
4) Ease of use
5) The form editor, issuing an xml file to build exactly the same form in the project (not to create everything from the code)
Minuses:
1) Minor bugs like a curve dragging forms with a mouse (if during the update you move the mouse over the area of the border of the form, then dragging stops, because of which you have to move it almost pixel).
2) Not too much functionality
3) Rare project updates
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Skinnable GUI library for XNA 4
GUI with abundant functionality, the ability to change the skins and other buns, however, the average complexity of development.
Pros:
1) Rich functionality
2) Ability to change skins
3) Open source
Minuses:
1) No documentation
2) Average complexity of use
3) The project is still in the betta stage
XNA Game Console
Game console.
Pros:
1) ease of use
2) Easy to add new commands
3) Open source
Minuses:
1) Does not work on xna 4
2) Looks like the project is no longer supported.
Alternatively, the project can be used, but only when processing to fit your needs. It is best to remove the visual part altogether, replacing it with one of the gui described above.
Box2D.XNA
Port of the popular physical 2D engine under xna.
ps There is an excellent
article with which you can create your own physical. engine
Pros:
1) Ease of use
2) Large community
3) Open source
Minuses:
1) There is no documentation (but in the discussion, many incomprehensible things are chewed in detail)
2) The project is no longer supported.
XNA 2D Particle Engine
Relatively simple motion for a particle system
Pros:
1) Good documentation
2) Easily embedded code
3) Easy to handle
Minuses:
1) Not very realistic particles
2) The project has not been updated since 2010
Mercury Particle Engine
Very functional particle system with effects editor and very extensive documentation.
Pros:
1) Very extensive documentation, there is even a
video - tutorial
2) There are releases for both xna 3 and xna 4
3) Good functionality
4) Pak textures supplied with the project is not bad
Minuses:
1) Medium difficulty in handling