If you area a software developer looking for your next gig, here area few sources for inspiration. I've organized this list into two main categories: paid and unpaid. The thinking behind this is that some developers would prefer to get paid while they learn about a particular technology or industry, others just want to find something cool to work on.

Paid

Demand Rush reminds me of a "reverse Patreon" where instead of you giving money towards a particular project, someone pays you a monthly subscription to complete their project.
Free Software Jobs is a job board where all jobs must relate to free software positions. In other words, if you are already doing some open source work, this might be a way to supplement your efforts.
Old Geek Jobs is designed for employers to know beforehand which applicants (35+) will apply, which makes those applicants feel comfortable applying.
Finding something to sell on Alibaba
Your best passive income has a ton of neat ideas.
Indie Hackers has this awesome graph that shows you how much companies are making.

Unpaid

If you're not afraid to copy, Product Hunt has a ton of great ideas.
Github is world class for ideas. I find interesting projects on Github all the time.
Former Music Hack Days are great places for inspiration. I specifically look for presentations,
videos, recaps and winners.

I'll keep adding to this list as time continues. If you have any suggestions, please add them below.