What are good collaboration options for a software development team?

communications.
Sounds stupid, but this is essentially the core. 

Yes, thats true ;-)

I was also wondering, what are some Appian built-in capabilities to assist teams 

like shalini said: an information message when another user is editing the same object
Versioning for almost all elements
what else do you looking for?

Honestly, I'm not exactly sure, that's why I'm asking. Maybe something like:

• Adding description to versions
• options to define and monitor sprints/ development progress
• code sharing accross applications
• how-to)organize users into project teams
• linkage to (external) project management tools, like a kanban board or jira
• nominate for peer review
• tag for deployments
• feedback option for developers
• ... 

Honestly, I'm not exactly sure, that's why I'm asking. Maybe something like:

• Adding description to versions
• options to define and monitor sprints/ development progress
• code sharing accross applications
• how-to)organize users into project teams
• linkage to (external) project management tools, like a kanban board or jira
• nominate for peer review
• tag for deployments
• feedback option for developers
• ... 

BE.Thomas said:

Adding description to versions

Description changes are saved (and shown) along with the version history.  Designers just need to remember to update the object's description if that's a requirement of your dev flow.  For me it's usually been an optional thing.

I assume, there is no option to make a description (or the change of) mandatory  

correct, and considering that changes to objects like interfaces and expression rules can be made easily & very often, it would be a bad idea (IMHO) to mandate such a thing.  it would be up to the dev team leadership to ensure devs enter a "recent version change" comment in the description when they're done their changes for that day.  "requiring" updates to the description any more often than that would only increase clutter.

further, i find (other than major updates) this isn't a good use of the object Description field.  Instead it's very easy to just add a comment block (or annotation in the case of process models) to hold notable version-specific changes, which can include JIRA ticket numbers, etc.

Thank you, so that clarifies for me the place to hold such major update documentation.

That's a technique I used on a team for many, many years.  It always worked well.  To add to that, consider also an external object tracker that forces developers to check out and check in code, albeit not enforced by Appian itself.  We used an excel sheet, which isn't the best tool, but it got the job done for years.