While both Diffen and Wikipedia are user-generated repositories of information (encyclopedia, if you will) running on similar software engines, they are both quite different.
Comparison chart
 | Diffen | Wikipedia |
|---|---|---|
| Topics | Serious as well as frivolous allowed | History, science, popular culture, people, current events, fiction, etc. |
| URL | diffen.com | wikipedia.org |
| Founded in | 2007 | 2001 |
| Advertising | Yes | No |
| Owner | Diffen LLC | Wikimedia Foundation |
| Objective | Collection of differences and comparisons. | To inform people of public knowledge |
| Wiki engine | Mediawiki | Mediawiki |
| License | Diffen licenses its content under the Creative Commons (BY, NC, SA) license. | Wikipedia content is licensed under the GFDL and Creative Commons (A, SA) licenses. |
| Commercial? | Yes | No |
| Type of site | Wiki | Wiki |
| Slogan | Diffen. Discern. Decide | The free encyclopedia that anyone can edit. |
| Point of view | Neutral (facts). Opinions are allowed in the Comments section and in user ratings for certain entities. | Neutral |
| Purchase or Free | Free | Free |
| Number of articles | About 1000 comparisons, and information about over 5000 entities | 4.3 Million articles in English |
Objective of Wikipedia vs. Diffen
While the aim of Wikipedia is to be a online encyclopedia, Diffen's scope is to be an encyclopedia of comparisons.
It's a somewhat narrower scope because the articles on Diffen are not on a specific topic but on the difference between or comparison of any 2 things. For example, while Wikipedia has articles on LCD screens and Plasma screens, Diffen has an article on the difference between LCD and plasma.
While Wikipedia articles do often mention differences between similar things, and there are also some comparison articles — such as comparison of text editors — Diffen articles focus on comparing any two "entities.
Relationship between Diffen and Wikipedia
Diffen is not a part of the WikiMedia Foundation. There is no formal relationship between Diffen and Wikipedia.
As an information resource, Diffen complements Wikipedia for researchers interested in differences and comparisons.
Licensing
Content for Wikipedia is licensed under the GNU Free Documentation License (GFDL) and Creative Commons license. Diffen content is licensed under the CC-BY-NC-SA license.
References
WikiLeaks
Comments: Diffen vs Wikipedia