/r/serendipity is a meta-subreddit meant to broaden the perspective of its subscribers. It takes a popular entry from a random subreddit and posts it every few hours. If you want to increase your exposure to niche subreddits, or just your perspective on things on the web in general, serendipity might help you do that. But it might not. It's a bot, after all.
Serendipity requires PRAW.
build_subreddits.py requires lxml as well, if you want to update subreddits.
You'll likely want to stick these scripts in your cron, something to the effect of:
0 */3 * * * python /path/to/serendipity/main.py # Post a serendipity link every 3 hours
0 0 1 */3 * python /path/to/serendipity/build_subreddits.py # Rebuild subreddits list every 3 months