There was a small community of users who were building applications (mostly built with GTK+) that were often of higher quality than what I got used to on Android now. They could be installed via the App store equivalent or just using apt-get from the terminal.
There were some great "Whoa, this works?" moments, like running the full-blown Arduino IDE and flashing something via USB-OTG or writing a Python script that makes the phone act as a sonar. And everything almost with the ease of a Desktop-PC, just a bit slower :)
I went through four used N900s (they unfortunately aren't very durable) before I gave up and got myself an Android because the web became too bloated and slow. I still miss it every time I'm using my phone for anything different than calling someone or taking a photo. I just had to get that off my chest.
The fewer people who see a thing, the uglier the source is.
And as you go down the stack on mobile devices... there are very few people watching, indeed.
https://www.kickstarter.com/projects/2103809433/338898127?re...
It's less powerful than a smartphone, but designed from the ground up for hardware hacking.
disclaimer: I am part of the WiPhone project
It if weren't for the whole Linux vs Symbian, plus rebooting devenvs multiple times across Symbian and Maemo history, things would have turned out much different.
But like all major corporations, politics play a big role.