You may encounter new factions during your travels and adventures through Othonia.  Some of these factions have formed their own guilds, secret or otherwise. There are other subguilds which are more secretive or less populous and thus less well known, which are not found in this list.

There is no EXP cost to buy into a Secret or Sub-guild.  There is simply a Role-Play requirement.  Keep in mind that some NPCs might require certain tasks, missions, or donations in order to fully accept you as a new member.  

Membership in a Secondary Guild does NOT count towards your limitation of three guilds.

You cannot start a New Character with a Secondary Guild without explicit Plot approval.

Joining a secret or sub-guild will permit you to have a guaranteed a trainer for your Level 4 and Level 5 skills of that guild without having to dedicate actions towards finding one.

The existance of these guilds are known throughout Othonia.

Parent Guild: Thieves' Guild

Skills Taught:
Pharmaceuticals
Stealth

Parent Guild: Scholar's Guild

Skills Taught:
Architect
Historian

Parent Guild: Tinkers' Guild

Skills Taught:
Gunsmith
Mariner

Parent Guild: Athletes' Guild

Skills Taught:
Performance
Acrobat

Parent Guild: Patrician's Guild

Skills Taught:
Psychology
Socialite

Parent Guild: Landworker's Guild

Skills Taught:
Botany
Geology

Parent Guild: Homecrafter's Guild

Skills Taught:
Culinary
Woodsman

Parent Guild: Physician's Guild

Skills Taught:
Surgeon
Artisan

Parent Guild: Warcrafter's Guild

Skills Taught:
Gemforge
Armorsmith

Parent Guild: Explorer's Guild

Skills Taught:
Mariner
Architect

Parent Guild: Landworker's Guild

Skills Taught:
Artisan
Woodsman