SemVer 
SemVer is a very simple semantic version parser in Ruby. It takes a string and returns an object that can be validated and compared.
Examples
require 'sem_ver'
SemVer.parse('0.0.10').valid? # true
SemVer.parse('v1.0.10').valid? # true
SemVer.parse('X.10').valid? # false
SemVer.parse('1.0.0') > SemVer.parse('0.9.9') # true
SemVer.parse('1.0.1') >= SemVer.parse('1.0.0') # true
SemVer.parse('1.0.1') >= SemVer.parse('1.1.0') # false
SemVer.parse('1.0.0') == SemVer.parse('1.0.0-pre1') # false
SemVer.parse('1.0.0') > SemVer.parse('1.0.0-pre1') # true
...
Alternatives
If you need more advanced things, versionomy looks great.
Credits
Copyright © 2012 Sergio Gil, released under the MIT license