@TheFlame52:
Thank you very much, it is an honor. 
@Ruttiger:
While the anti-grind features limit crafting skills to 10 (“This task is too simple to train your (x) beyond (y).”), it’s still possible to get (some) combat skills to 20, as I did. Of course, there’s anti-grind for those as well, which exponentially reduces skill gain if you use them too much in a short time, but after almost 2 in-game years (and few RL months) I finally managed to reach 20 in Melee.
I tested the anti-grind in my “Zombie Shooting Range” (on Bear-Trapped zombies) with a BB Gun and 100 BBs (with a character who hasn’t used ranged weapons for over 1 in-game year) earlier today. With 1st 20 BBs he gained 0.2 in Rifles. After another 20, the skill only raised by 0.12. 3rd set of 20 BBs only raised the skill by 0.08, 4th by 0.05, and 5th by only 0.03. The skill-gain slowly recovers over time, so you can still slowly improve your combat skills by killing monsters as you explore, but you can’t level them up by just spamming them over and over.
The challenges are also updated every now and then to reflect the changes to the game (and to combat possible loopholes and exploits), as Flame mentioned.