Here's an ongoing, updated list of customizations/differences from classic live, on the server:
1. animist pet cast limit
2. Stat potion reuse timer
3. Custom items
4. More custom items
5. Charge values
6. Insta kill zone at border keeps
7. Housing merchants with no items
8. Pet's stop following players who stealth (1.88 patch)
9. Horseroutes in OF & Porttimer of 7 minutes instead 15
10. Ranges on conc buffs
11. Equipping poisoned weapons without Envenom skill removes poison
12. Remains droprate and taxidermist delay
13. /xp off
14. RR13 cap
15. Horses
16. Events and Event Rewards
17. Underwater in classic zones
18. /level command
19. Boats
20. Custom Siege engines
21. Being able to carry more than 214p
22. House rent payment from consignment merchant is disabled
For further descriptions of the items on the list,
go here!