<nick_one> !Add alpha
-Your_Bot- You are in the Alpha group
<any_nick> !group
<Your_Bot> [Group] Alpha 1 users [Group] Beta 0 users
<nick_one> !Add beta
-Your_Bot- You are in the Beta group
<any_nick> !groups
<Your_Bot> [Group] Alpha 0 users [Group] Beta 1 users

Code:
on $*:text:/^!add (alpha|beta)$/iS:#:{
  var %g $regml(1)
  notice $nick You are in the %g group
  set $+(%,%g) $addtok($($+(%,%g),2),$nick,32)
  %g = $iif(%g = alpha,beta,alpha)
  set $+(%,%g) $remtok($($+(%,%g),2),$nick,1,32)
}
on $*:text:/^!add\b/iS:#:msg # Invalid Parameters. Use: !add alpha or !add beta
on $*:text:/^!group(s)?$/iS:#:msg # [Group] Alpha $numtok(%alpha,32) users [Group] Beta $numtok(%beta,32) users