This should give you a good idea: http://forums.bukkit.org/help/bb-codes
A MacBook Air isn't the best computer to run a server on, but it will work.
Use this in your start.command
Can you make a list of your plugins?
What does canyouseeme tell you? http://www.canyouseeme.org/
Do you have an antivirus program blocking it?
No players, except you, can connect...
Well because it's not updated to 1.3.1.
Find the pre release here: http://dev.bukkit.org/server-mods/essentials/files/
Note: Is not stable, may...
Found triplicate: http://forums.bukkit.org/threads/players-cant-use-plugins-unless-op-help.91559/
Dupe thread http://forums.bukkit.org/threads/please-help-plugin.91570/
Btw, typing in all caps in the title doesn't help anyone...
Check your ops.txt
No. Apple Airport Extreme routers are FAR different than your average router. I have one myself.
Pex isnt up to date.
Bukkit doesn't support offline mode servers. Buy the game, and have your friends buy the game.
Delete the 3 world files. Put in your world. Run the server. Done.
Your server is 1.2.5, their client is 1.3.1
They can't connect. Either update the server to a Dev Build. Or Downgrade the clients.
The plugin OpenWarp v1.1-b115 (rev d4486a88
e3b812fd4ead71c3275a15ed897570be) (Is it up to date?)
Probably because your server is 1.2.5 (Since the update wont work for you) and your client is 1.3.1
Remove these and wait for their updates:
RpgEssentials v1.2.10 (Is it up to date?)
pvparena v0.7.23.1 (Is it up to date?)
Edit: Wboops. Already...
Separate names with a comma.