Apple - Can HomePod be controlled using anything other than Siri?

I'm specifically hoping for some sort of remote control app for iOS.

The standard Music app can be put into a mode where it acts as a HomePod remote control: the user can queue individual tracks and playlists, and the HomePod will play them using its own connection to Apple Music and the iTunes Music Library.

It is a little tricky getting the Music app into that mode.

One way is to open the Control Center, then long-press or force-touch on the music control. This reveals separate control panels for your iOS device and any other controllable devices, including AppleTV and HomePod. Tapping the HomePod will open the Music app in HomePod-control mode.

The HomePod User Manual tells you everything you need to know.

Control HomePod

You and anyone in your home can control HomePod using Siri, or by tapping the top of HomePod.

To control the HomePod, you have three options only:

• the top of the device
• Siri
• Apple Music (limited to playback control)

You can use the HomePod as:

• speaker phone (make/receive calls through Siri - Siri, call Mom)
• stream music from iTunes via AirPlay
• Listen to Podcasts, News
• Use Siri's personal assistant feature (Siri, set an appointment for dentist)
• Control your home (HomeKit)

The HomePod App is used to change the settings, not to control it.

HomePod settings

The person who set up HomePod can use the Home app on their iOS device to change HomePod settings. There are settings you specify for each individual HomePod you have, and settings that apply to all of the HomePod devices in your home.

According to Apple's HomePod site, it can be controlled using Siri and the Home app.

For example, here's one of the sections on that page:

Just say “Hey Siri, turn on the lights” or “Hey Siri, make the room cooler.” You can even ask Siri to set scenes, like “Good morning,” that put multiple accessories to work — all at once. A wide range of accessories work with Apple’s HomeKit platform. Just add an accessory to the Home app, then control it with your voice on HomePod.

Apple doesn't mention any other type of control other than the buttons on top of the unit, Siri, and the Home app.