Here is my program Oasis. It is for this challenge. http://tibasicdev.wikidot.com/forum/t-164477#post-628597

Oasis is a basic shell that will run basic programs.  It uses Celtic III.

Let me know what you think.

Now if only I had a calc to test it!

lol

I was inspired a lot by mirage.
Also, I wanted to prove simple homescreen graphics can look nice.

Very awesome!  Nice and simple interface with functionality as a preference

I wonder, for games that uses Return instead of Stop to exit completly, does these games can exit back to the shell without causing problem?

Return works, but not Stop.  Since Return returns and Stop stops... 

Well, what I was wondering more is: can variable conflicts occurs? I mean, if the shell uses a variable or list in particular, then the game overwrites it, then when it returns to the shell, a RAM clear occurs due to a bad variable value used with Celtic III

Nope, cleaver coding prevents that.  I back up my variables needed in the AppVar that I store the Hot Keys in during program execution.  The stop dosn't remove these, so it will mess with stuff, though not bad enough for a RAM clear.  It just messes up your hot keys.  If this happens, you can just delete both AppVars.

Simple but nice.

BASIC Shells aren't a new idea but these new ones are actually very good.