I know that there has been another project on this, but I wanted to put my version of it here. I think of it as completely different and won't interfere with already created scoreboard commands that much, as well as easy to understand. This is best used for small, private servers.

(The inspiriing post is http://www.planetminecraft.com/project/tpa-command-in-vanilla-minecraft/)

Instructions:

First, do this in chat:
/scoreboard objectives add tpa trigger

The uppermost left-side command is:
/fill ~ ~-1 ~ ~ ~-1 ~1 redstone_block (you may have to change the z or x axis depending on the position of your block)
The lower left-side command is:
/fill ~ ~1 ~ ~ ~1 ~1 air (same note as above)
This created a command block clock.

The uppermost right-side command is:
/scoreboard players enable @a tpa
This enables all players to use the /trigger command for tpa. (Non-ops can do /trigger as well)

The lower right-side command is:
/tp @a[score_tpa_min=2,score_tpa=2] @a[score_tpa_min=1,score_tpa=1] 
This teleports players with the score of 2 to players with the score of 1.

That should lead to a comparator (see picture) with the command:
/scoreboard players set @a[score_tpa_min=2,score_tpa=2] tpa 0
This resets the player who's score is 2 so he/she is not constantly teleported and the comparator can reset.

If everything works out, players can do this:
/trigger tpa set 0 
This makes the tpa command not work if someone tries to tp to you.
/trigger tpa set 1 
This makes you able to be teleported to, this is the equivalent of /tpaccept
/trigger tpa set 2 
This makes you teleport to a player with score of 2.

Then, for simplicity do /scoreboard objectives setdisplay list tpa
This makes all players see who has what score.

Pros:
Not overcomplicated (perhaps too easy)

Cons:
No fancy stuff like msgs, but I'm sure others can adapt upon my basic module to do that!
No actual "NAME wants to teleport to you"

To those who wish to use it, go ahead!
I apologize for my nooby posting, I am relatively new to forum posting.

Leave a diamond if you really enjoyed it!

Drakonkinst