[zokier]

There are lots of semi-related issues raised in your post.

Generally copying/cloning a design is legally OK, but copying the implementation/execution of that design is not OK. This is well demonstrated in the font industry. You can copy a typeface as long as you do it "cleanly" (ie by not reverse engineering the font files), which is why there are lots of cheap copies of common fonts. This is probably the most relevant aspect for this project. They can copy the look'n'feel of Trello as perfectly as they can, but they can not copy Trello assets, CSS etc.

Then there is the Ribbon. Being software Microsoft has it patented which makes clones of Ribbon more in the gray area. On the other hand the enforceability of such patents is somewhat questionable.

Lastly the games. In addition to copyright infringement I suspect there is also risk of trademark infringement. What makes trademarks interesting that they are thought to need enforcing to remain valid, so companies generally are less willing to a blind eye to tm infringements. Also unlike copyright which considers where the work comes from, trademarks generally consider only what the work looks like and if it can be confused to the original trademark.