The only non heading broccoli I have tried is Aspabroc this past spring and fall. It is very good with a slight peppery taste. The stems are the best part and are very tender. I'm not sure how long you can harvest it for. I've grown it in the spring started in early April and harvested from early May until early June when it was pulled to make room for other crops. In the fall I set out the plants on August 12 and started harvesting in early October and continued until around Thanksgiving IIRC. Aspabroc has a smaller footprint and grows taller than heading broccoli so you can plant it at about 8" spacing with no problem.

Are you more looking for the broccolini varieties or perhaps broccoli rabe types? Neither are true "Broccoli" (brassica oleracea italicais). Apollo is "Brokali Apollo", a cross between broccoli and Chinese kale but it usually forms a small primary head and then side shoots will develop. Same for Piracicaba - broccolini that forms a small central head plus many side shoots.

Broccoli rabe forms no head.

Dave

The spouting broccolis form side shoots with minimum central head. Many of the older heading broccoli varieties also produce side shoots for an extended harvest. One the more popular is Green Sprouting Calabrese. https://www.southernstates.com/catalog/p-8246-broccoli-green-sprouting-calabrese.aspx  . There are also Purple Sprouting and White Sprouting varieties. Aspabroc was the original broccolini. Since that introduction several developers have introduced broccoli Chinese kale crosses. In addition to Apollo and Piracicaba There are Artist, Atlantis, Happy Rich ... There is also a leaf broccoli Spigariello Liscia, never tried it. probably similar to kale.

I bought some seeds sold as gai lan at Johnny's. They were not gai lan at all but everyone involved in our garden was very pleased. Robust plants that, for 50 plants, generate maybe 10 small broccoli heads a week for several months. Doubling to 100 plants or more next year. Also, this variety is not brassica oleracea, because it has white flowers.