We're hoping to have the d20 mechanics complete in the beta release, that is:
- classes*, including abilities gained by leveling
- skills [still discussing the form, though]
- saving throws*
- attack rolls and AC*
Other main features include:
- some items (including magic items) *
- some monsters*
- some spells*
Things marked with an asterisk are already in.
Everything else is just window dressing. For example, highscores and encumbrance are in, but do not work properly yet.
Once the basic mechanics are complete, we can freely add more classes/feats/skills/monsters/items/whatever.
EDIT: We're discussing how to code in multiclassing and prestige classes, so they are bound to show up sometime, but I'm not sure they'll make it into 0.1.