FOSS projects are mostly developed on a volunteer basis.
This makes the currencies by which they are developed: free time and motivation.
Often times you have the free time, but not the motivation. Often this is not from feeling that the work isn't worth doing, but that you feel inadequate to do it.
Don't be disheartened. There's plenty you can do that helps.
Just be there, whether in-person or online.
You can do whatever else you want while being there, but it's encouraging to not be along in your endeavours.
You may even find some motivation of your own.
When others are talking about what they want to achieve, respond enthusiastically.
It makes them more likely to follow-through and do so, and in the very least makes them feel good.
This does risk making them feel worse if they never get around to it, but sometimes that's sufficient to shame them into action later, and other times it's sufficient to say "these things happen".
Engage in discussion about what others want to achieve.
It's extremely valuable for refining ideas, so they can implement what they want to do better, it keeps it fresh in their mind so motivation lasts longer, and it leaves a clearer idea of what to do so it may be completed before motivation runs out.
Mention what other people are doing to people who might be interested.
You could end up with anecdotes of other people thinking it's a cool idea, which when relayed to people doing the work provides their own motivation.
Remind people of the successes they've had.
It makes people feel good about what they've already done, and can put any issues they are currently struggling with into perspective.
Lars pointed out that Yakking has published more than 180 articles at a rate of one per week! We've managed to get this far, we can continue for a good while yet.