Probably the most similar group would be the seventh-day adventist church, which came out of the "second advent movement", the same movement which eventually spawned the watchtower magazine.
Some similaries:
1. Multiple specific dates set for the end of the world. I may post these later.
2. The "end" will come within the lifetime of the "1844 generation" (Wow- thats familar! JWs say 1914 generation)
3. The initial prediction of Christs return to rule the EARTH in 1844, later changed to an "invisible" presence in HEAVEN. (Same as the JWs only different year)
4. Churchs rejected for not accepting 1844 date. (JWs reject churchs for not accepting 1914 date).
5. Their church alone is composed of the remnant of the 144,000 from the book of Revelation.
6. The early adventists took no "name" and had no "organization" later they got both of these. (same as JWs who initially rejected the concept of a distinctive name and organization, and who now relish in these things.
7. extensive emphasis on chronology.
8. all former members "apostate"
The above information can be found in the early chapters of an older book called "Seventh-Day Adventism Renounced" If you can get a copy of this book and can go though some points of it with a JW (they shouldn't object to this as it doesn,t specifically mention their group) it should prove DEVASTATING to the mind of the JW.